Hello … and welcome 
Of the three outlets you mentioned … I personally would tend to avoid FBM for several reasons. While I recognize that they are “cheap”, the consistency of their product and product descriptions are questionable at best and I believe that they often misrepresent what they are selling. IMO … knowing the “ingredients” of the mattress you purchase and knowing that the layers are correctly described and the correct firmness and type of latex for your needs is a big part of “getting it right”. For me … FBM and its alternative companies are like rolling the dice.
Of the other two … there is no doubt that SleepEz represents better value than Pure latex Bliss. They also have more selection in terms of mattress construction and layering and since they offer the exact same foam as PLB … there is no doubt in my mind which I would choose. PLB is great for testing purposes to see what type of layering works for you and is among the best national brands but I would “duplicate” the construction of the model I liked best through a DIY outlet like SleepEZ because of the better value.
Your husbands shoulder pain is fairly common for his body type in men. The shoulders are wider than the hips and need to sink in further for correct alignment yet the hips are heavier so have a tendency to sink in further. This means that the layering is very important and that the top needs to be soft enough for the shoulders too sink in far enough without causing pressure and numbness/pain. The correct pillow can play a role here as well (side sleeping needs a thicker pillow to keep the neck in alignment and also helps to relieve the pressure on the shoulders slightly).
Another alternative for a DIY mattress is a construction that uses a type of zoning that puts softer foam under the shoulders/torso and firmer foam under the hips. While this is not always necessary with latex which has a higher support factor or progressive firmness than other foam materials … it can certainly make a big difference in more difficult or problem cases. A member here that specializes in this type of DIY construction is http://www.customsleepdesign.com/.
Both SleepEZ and Custom Sleep Design can split the mattress construction side to side so that two people sharing the same mattress can customize each side as well.
In terms of the comfort layers … normally a good starting point for side sleeping is a 3" Talalay comfort layer in the range of 19-24 ILD. In your case … on the softer side may be better because of your lighter weight. In his case … slightly softer may also work well to allow for his shoulders to sink in far enough when he is side sleeping. 19 would seem to be good choice for both of you which also happens to be very similar to the Nature.
In terms of the support core … Both Dunlop and Talalay latex would work well and with a 3" comfort layer I would recommend firm for both of you. In your case … a firm Talalay or Dunlop for the next 3" layer and then an X firm Talalay or Dunlop for the bottom 3" would likely work well. In his case … I would recommend firm Dunlop for the middle 3" layer and X firm Dunlop for the bottom 3" as Dunlop has a higher support factor than Talalay which would be important for his heavier weight and better for keeping his hips from sinking in too far relative to his shoulders if the mattress did not have shoulder/hip zoning. Dunlop would have a slight edge in this regard over Talalay.
This would be similar to the Nature in terms of comfort but more supportive in the support layers. Just to let you as well … the Nature PLB uses Talalay in the support layers rather than Dunlop.
If you go with shoulder/hip zoning … I would start with the nature as a baseline and then follow Bob’s (the owner’s) recommendations based on your discussions with him. This would allow your husband especially to choose a firmer comfort layer under the hips (say 24 ILD) and a softer comfort layer under the shoulders (say 19 ILD) to allow them to sink in further for better pressure relief without sacrificing hip support. (say 19 ild).
Custom Sleep Design is 11" of latex so it is thicker and more expensive but would be more personalized for both of you in terms of comfort and support. SleepEZ would have 9" of latex (in the 10000 model which I would recommend) and not have the shoulder/hip zoning but would also be less expensive. It has the same amount of latex as the PLB.
I am assuming/hoping that you both tested the PLB Nature for both comfort and support using guidelines along the lines of the “Five steps to your perfect mattress” pages on this website. While you can ignore the parts of the comfort and support pages that talk about choosing materials since you have already decided that latex works well for you, knowing how to test a mattress for both pressure relief and support/alignment inependently is a really important part of field testing.
It would be well worth testing the PLB pamper with the 2" topper on top of it for comparison purposes as it may work well as well for one or both of you in terms of preference. The topper is 14 ILD which would be on top of 1" 19 ILD on top of a firm support layer totalling 9" of latex as well so it would be similar to the Nature with the same support layer but a softer comfort layer of the same thickness.
I hope this helps and if you have any further questions feel free to post them. I would be particularly interested in any comments you may each have regarding a comparison between the Nature and the Pamper with the 2" topper (along the lines of the testing recommendations mentioned earlier) as it would certainly help to determine the construction type of a "non hip/shoulder zonemattress which would work best for you both and the ILD of the comfort layers you may each prefer.
Phoenix
PS: If you register for the forum here and then have at least one post using your registered name … then both SleepEZ and Custom Sleep Design (like all other manufacturing members of this site) will give you an additional 5% discount on your mattress.