Hi kenshireen,
I don’t know anything about your body types (weight/height etc) or your sleeping position but you did mention that your husband spent at least some time on his stomach in which case I would be very cautious about the Beautiful or the World’s Best Bed (either with or without the 4" latex foundation). These are mattresses that would be best for people who slept on their side and in other sleeping positions they could be quite risky for alignment … particularly for heavier people.
The prices you mentioned for the PLB Nature plus the 3" topper are also on the high side even compared to the MAP (minimum advertised price) for PLB which is already higher than many manufacturers who make all latex mattresses (such as Tucker). The Nature has a MAP in the range of $3499 (king set) and the 3" topper (in king size) is @$589 (or $599 in the Active Fusion version) which together comes to under $4100 so I’m not sure where the extra cost is coming from. Because this is the minimum advertised price (which is controlled) … this is the most they should sell for and even here it is significantly more than other options you have (including Tucker) that would be significantly less for a similar amount of latex (the Nature is 10" of latex and then a topper and the Tucker is 9" of latex and a topper).
If all else is equal … I would also tend to go with firmer choices rather than softer choices because as you know you can always add a topper to a mattress that is too firm but if you buy a mattress that is too soft you’re stuck with it (and the back aches it can cause).
A fair price IMO would be in the range of about 20% - 25% more than you could buy a similar mattresses from an online merchant (this takes into account the lower risk involved in buying a mattress that you can test first). To give you an example … there are several 9" latex mattresses available in the list of online manufacturers that are members here (see post #21 here) that are under $2000. Any of these plus a foundation and a 3" topper (if this was even necessary) would be significantly less than the PLB. They also have the advantage in many cases of being able to customize the layering choices or either re-arrange layers or exchange them.
Out of the local choices you mentioned … I would certainly go with Tucker mattress (and their 2" topper or with a topper purchase elsewhere depending on the softness you want and pricing) because I am guessing it is much better value (based on my conversations with them). There is no point in paying for an amount of latex which has no benefits or improved feel and performance for you (and again this would depend on your body type and sleeping positions and on any differences you felt between mattresses). The Tucker mattresses also have the advantage of being two sided and flippable which will extend their life even with a material as durable as latex (and of course is more costly to make when the mattress is finished on both sides).
You would need to know the layering of the Nature and then tell the manufacturer you were dealing with what it was so they could help you choose the model that they carried that would be the closest approximation (they wouldn’t be an exact match because they may not offer mattresses with the same layer thicknesses or layer ILD’s as the PLB). They could also help give you feedback about the suitability of this layering for your body weight and sleeping positions based on the averages of their customer base with similar circumstances.
You can see the construction of the old version of the Nature here
The new version has removed the bottom 1" layer and added it to the second layer. I don’t know the layering of the new Nature for sure but a reasonable estimate would be …
2" of Active fusion Fast Response talalay 21 ILD
2" of Blended Talalay 28 ILD
6" of blended Talalay 36 ILD
I would also consider a slightly firmer topper in the range of 19 - 24 ILD rather than the very soft 14 ILD (although again this would depend on body type and preferences).
While the PLB mattresses are very good quality, without a significant discount (which are often available with retailers that still have the old models) … I wouldn’t consider them at this price unless there was a compelling reason to do so outside of “value”.
With a side to side split … each half of one or more of the mattress layers uses a different firmness level of latex and they are all enclosed in the same cover. In effect you have two mattresses in one. There is either a quilted cover or a latex layer over any split layers to even out the feel of the split itself.
You can read a little more about the benefits of split layers in post #2 here and some of the ways that can be used to accommodate a couple with very different weights or needs and preferences are in the beginning of post #2 here.
Phoenix