Hi Pappy,
In theory no … none at all. You can see in post #14 here that there may be some potential benefits to a thicker mattress for heavier weights or certain circumstances or preferences (assuming that the materials are high quality). I would also make sure that any foam you use is high quality … particularly in the upper layers (although I’m guessing that by “foam” you mean latex?). There can also be some benefits to having more layers to re-arrange or exchange which you can read about in post #2 here although it can also add complexity which can make finding the best combination more difficult for some and there are some combinations that wouldn’t be suitable (such as too much soft foam on the bottom).
I’ve never used it personally but for those that just want the benefits of torso elevation I think it’s a good and economical solution. I’d probably also get a one of their wedges for under the knees so you can achieve the zero gravity position. You can see a comment from someone who used it (and also built their own DIY mattress to match the Pure Latex Bliss Nature and Nutrition) in this post.
Phoenix