Hi scoaste,
Welcome to the Mattress Forum! 
I’m assuming that you’ve read the mattress shopping tutorial (which is the first place to start your research) but two of the most important links in the tutorial that I would especially make sure you’ve read (just in case you haven’t read them yet) are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you.
While I can’t speak to how any mattress will “feel” for someone else because this is too subjective and relative to different body types, sleeping positions, and individual preferences, sensitivities, and circumstances … outside of PPP and how well you sleep the most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t see or “feel” and assessing the quality/durability and useful life of a mattress depends on knowing the specifics of its construction and the type and quality of the materials inside it regardless of the name of the manufacturer on the label (or how a mattress feels in a showroom or when it is relatively new) so I would always make sure that you find out information listed here so you can compare the materials and components to the quality/durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else.
Because your own personal experience is the only way to know for certain whether any mattress will be a good “match” for you in terms of PPP … the exchange/return policy (and any costs involved) can also be a more important part of the “value” of an online purchase just in case (and in spite of the “best judgement” of everyone involved) the choice you make doesn’t turn out as well as you hoped for.
In terms of the quality and durability of the materials …
The DreamFoam Mattress Ultimate Dreams 13-Inch Gel Memory Foam: contains …
3" of 4lb Gel memory foam
2" of 5lb Memory foam
8" of 1.8lb HD Polyfoam
Their descriptions and comments indicate that this would be similar to the Tempurpedic Cloud Luxe in terms of firmness (possibly a little firmer).
They have a 45 day trial period with a $99 cost to return or exchange the mattress.
There are no lower quality materials or weak links that would compromise the durability or useful life of this mattress relative to your weight range.
The PlushBeds 12" Cool Bliss Gel Memory Foam: contains …
3" of 4 lb gel memory foam
2" of 100% natural Dunlop latex
2" of 2.5 lb convoluted polyfoam
5" of 2.5 lb polyfoam
With the 2" of latex under the top layer of memory foam it would likely have a more resilient (springy) feel than a mattress that uses 2 layers of memory foam.
They have a 100 day trial period which costs nothing to return the mattress unless you open any bonus items in which case the cost is $99.
There are no also no lower quality materials or weak links that would compromise the durability or useful life of this mattress relative to your weight range either.
The Alexander Signature Select: contains …
1" - 1.5" polyfoam quilting (depending on the firmness you choose)
2" of either 4 lb or 5 lb convoluted memory foam or 2" of non convoluted 4 lb memory foam (depending on firmness)
2" of either 5 lb convoluted memory foam or non convoluted 4 lb memory foam (depending on firmness)
8" of 2 lb convoluted polyfoam
The soft would approximate the firmness of the Tempurpedic Cloud Elite or Cloud Luxe, the medium would approximate the firmness of the Tempurpedic Cloud Supreme, and the firm would approximate the firmness of the Tempurpedic Contour Elite.
They have a 101 day trial period which allows you to donate the mattress to a local charity for a complete refund at no cost or have it picked up for a $75 cost.
I would be somewhat cautious about the two layers of convoluted memory foam layers in the soft version which would be less durable than a solid layer of the same material although overall they would likely still be OK and wouldn’t be a weak link in the mattress that would compromise the durability or useful life of this mattress relative to your weight range either.
The Saatva Plush Soft:
I’m guessing that you are referring to the Loom & Leaf (which is made by Saatva) rather than the Saatva innerspring mattress (the Saatva mattress is a completely different type of mattress from the other three you are considering).
If this is the case you can see some comments about it in post #2 here in the simplified choice mattress topic.
They don’t include any information about which of the Tempurpedic mattresses it would be closest to.
They charge a delivery fee (probably under $100) and have a 75 day trial period which only costs you the price of the original delivery which isn’t refundable.
It also contains some materials (convoluted 4 lb memory foam in combination with the 1.5 lb base layer) that are lower quality/density than I would normally like to see in this budget range although they would also probably be OK for your weight range as well.
In terms of durability I would rate the PlushBeds 12" Cool Bliss Gel Memory Foam first and the DreamFoam Mattress Ultimate Dreams 13-Inch Gel Memory Foam next and then the Alexander Signature Select (soft) and the Loom & Leaf.
Phoenix