Hi nimailni,
Well you’ve certainly been doing your homework 
I’ll make a few comments that might help …
Houston Mattress Factory:
I sure wouldn’t have any trust issues with them. They’ve been in business for over 50 years and they have an A+ rating with the BBB (no complaints) which is almost impossible if you are not a member (which they’re not). They use high quality materials in their mattresses but there are also two different types of law tags. The state law tag is the one that lists the percentage of the ingredients and this will show latex (if it is). The other one may have shown SenSurPedic which is their trademark. They will also often add a polyfoam rail or encasement to the edges of their latex mattress for those who want a firmer edge but this is up to each customer (they custom build for each person). The all latex mattress they sell is also two sided which increases the value. I personally would trust what they say is in the mattress and the “correct” law tag should confirm it. I do know though (and you’re not the first to comment on it) that their building is not the most attractive “showroom” but the value of their product is great IMO and reflects that their money goes into their mattress and their willingness to make adjustments until you’re happy.
Angel Beds
They have some good choices and “better than average” value as well. Their mattresses are either a Dunlop core, a Dunlop/Talalay mix, or all Talalay. the difference with them is that the mattresses are 'standardized" which means that they have a standard layer thickness and ILD so they can’t be adjusted … only exchanged for a completely new mattress. In effect they have 4 different models rather than the dozens that individual adjustments of materials and layer ILD’s would provide. different layer thicknesses and ILD’s and different ticking/quilting layers can make a big difference in the performance and feel or a mattress including latex mattresses. I’m notsure which ones they had on the floor there but most people will describe Talalay as more springy while Dunlop will be denser and a little less lively. With a combination it will depend on the layers which of the different “feels” will come through the most.
Texas Mattress Makers
I like them as well although as you mentioned they don’t make an all latex mattress. The quality of each mattress would depend on knowing the specifics of the materials that are in them but they are also “better than average” value in each price range. With larger manufacturers … it’s important to find out the density of any polyfoam or memory foam layers in the mattress (the materials are a big part of the quality of a mattress and there are many types of polyfoam from very cheap to expensive which can feel similar in a showroom) but Noah is better at letting their customers know this when they ask than most.
Ikea
Ikea is also better than average value IMO although I would focus on their “mostly natural” latex rather than their mostly synthetic models. Even though the prices are slightly higher … they have better value and performance in a Dunlop mattress. The greater natural elasticity of natural latex works to the advantage of Dunlop latex. My thoughts about the Ikea latex lineup are in post #3 here. The Edsele is one of the better value choices at Ikea and it is certainly also “better than average” value even though the Dunlop latex is “mostly natural” rather than “all natural”. While most people would find this too firm and would prefer a comfort layer for better pressure relief … for those who like the feel of firmer Dunlop this would make a good choice.
Mattresses For Less
Not much to say here except that as you mentioned in these types of outlets … a “latex” mattress is not usually latex and will often have just a few inches of latex in the mix. If they are a major brand (like Sealy or Stearns and Foster) … then this latex will usually be “mostly synthetic” Dunlop which is the lowest cost/quality version of latex. These are the types of outlets I would tend to avoid.
Dump
Some of my thoughts about the Dump and other liquidation outlets are in post #3 here. Restonic is a licensing group of factories across the country and each factory can use different materials and layers in their mattresses which are sold in different areas of the country which is why they don’t list the specs on their website. All of the different versions may share the Healthrest name … but be very different mattresses. Some of these licensees do make an “all latex” mattress like you describe and some use several inches of polyfoam over the latex (which is not so great) and some use a 2" layer of very firm polyfoam in the base (which is fine and can help to “stabilize” a mattress with softer talalay and make it easier to construct). An example of a Restonic licensee which lists the layers of their local mattresses and makes an all Talalay latex mattress (both one and two sided versions) is Clare Bedding here (click the “view product information” link). I wish all manufacturers would be as open about what they put in their mattresses. If this mattress says 100% latex … then it may be one of the better choices … but I would also check to make sure it has a manufacturers warranty that can be registered with Restonic or the odds are pretty good that you are looking at a comfort exchange or a mattress that is “unknown” in terms of what has really happened that led to it being sold at the Dump. If this really was a new mattress set with a factory warranty with 8" of Talalay latex, then it would be good value.
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You have some great choices around you … and thank you for sharing your experiences with us
Phoenix