Hi tbonecopper,
I’m glad you found us before you ended up making an unwise purchase 
Outside of testing a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences) a mattress is only as good as its construction and the quality of the materials inside it. The information you would need to identify any weak links in a mattress is in this article and once you know this then you can compare the foam densities to the guidelines here.
They don’t list the density of the memory foam they use but I believe it’s in the range of 3 lb which is a low quality material and that in combination with the lower coil count of the pocket springs means that this mattress would probably break down fairly quickly with your weight (or even someone that was considerably lighter) and I would avoid the Hultsvik completely.
The latex in the Holmsta is a more durable material than the memory foam in the Hultsvik but I would want to know the specifics (such as how thick is the latex layer) and once again you would still have a relatively weak spring underneath it and even though the springs aren’t normally the weak link in a mattress … in your case with your higher weight and the relative thinness of the latex (which you would need to confirm) it would become a more important factor in the durability of the mattress. I would tend to avoid this one as well.
You can see my thoughts about online mattress reviews in post #13 here and as you can see they are among the worst ways to choose a mattress. I wouldn’t pay much attention to them because most of the people who review a mattress have little idea of the quality of the materials inside it and don’t have much knowledge about mattresses in general. In addition to this … each person can have a very different experience on the same mattress so what is “perfect” for one person may be completely unsuitable for someone else to sleep on.
Reviews about the transparency, knowledge, experience, and service of a store can be helpful but reviews that only talk about other people’s experiences on a mattress would have little relevance to you.
You can read an analysis of the Saatva mattress in post #1 here and a forum search on Saatva (you can just click the link) will bring up more information and feedback about them as well.
Both Brooklyn Bedding and Dreamfoam are sister companies (see post #3 here) and are members of this site which means that I think highly of them and they compete well with the best in the industry. They are also both in the list of the better online retailers and manufacturers that are linked in the tutorial post (in the optional online step). With your higher weight though I would make sure that you pay particular attention to the density of the foams in your mattress because a mattress that would be durable for someone who was lighter would be less durable for you.
Whether you need to increase your budget would depend on the types of materials you prefer but if you are most interested in specialty foams (memory foam or latex) then it would probably be a good idea to increase it somewhat yes.
Post #2 here also has more information about choosing a mattress for those in higher weight ranges that may also be helpful.
If you follow the steps in the tutorial post one at a time (without skipping any) you will have the highest chance of making a successful purchase. If you let me know your city or zip code then I’d also be happy to let you know of any of the better options or possibilities I’m aware of in your area.
The “basics” are to make sure you test a mattress carefully and objectively for PPP (or if you can’t test it in person then you would need a more detailed conversation on the phone with an online manufacturer or retailer) so that you know a mattress is suitable for you (see mattress firmness/comfort levels in post #2 here).
Once you are confident that a mattress is suitable for you in terms of PPP … then you need to make sure that you know the specifics of the materials inside it so that you can also make sure that the mattress would be durable for you.
Once you have confirmed that any of your finalists are both suitable and durable and you are choosing between “good and good” … then you can make a final choice based on the parts of your personal value equation that are most important to you.
Phoenix