Hi PeliasRex.
Welcome to our Mattress Forum! And most importantly … Congratulations on selecting your very first latex mattress and on making some very sound decisions :)!
It looks like you did some good research and ended up with some great choices … which of course is the ultimate goal of the site. As you know the all latex bed from SOL is a great quality value choice and you probably are aware that I think highly of them and consider to compete well with the best in the industry. They are knowledgeable and take good care of all their customers.
As with any foundation, I generally recommend checking with the mattress manufacturer/retailer to make sure that the support system you are considering wouldn’t invalidate the warranty of the mattress. This being said, the Glideaway Space Saver frame is one of the better metal frames which with its 14" height from floor to frame has certainly much more storage space than other brands/models. It also has four corner brackets included for attaching headboards and/or footboards to bed base which might be useful.
The GlideAway SS has a sturdy construction and supports up to 1200 lb (You’ll need to do the math and add the weight of the mattress and the people sleeping on it.) but I agree with you that this particular model has smaller gaps between the wires creating a more evenly supportive surface than some of the other similar platform bedframes. At a quick glance is also looks like Luma sells it for the best price on the market at the moment.
As far as the rug or the lattice layers you are considering, either could be used to ensure that the latex is evenly supported and that the under mattress ventilation is adequate, You wouldn’t necessarily gain much (if anything) by adding multiple layers … in fact another good solution for those with a more restrictive budget is to get some woven thick fabric (non-stretchy) and attach it as tightly as possible to the top of the wire grid so that the surface was more evenly supportive. Others even purchased a good quality cover and used it to the same effect.
The 1" bed rug made of coconut fiber (coir) with natural latex from Savvy is a porous mat allowing for air good circulation as well as preventing the wire grid “slicing” into the bottom of the mattress. The coir is usually placed to provide air circulation around the mattress, which with a wire grid foundation wouldn’t be a problem anyway. A vinyl lattice would be much thinner, but equally supportive The diamond lattice gaps would allow for both air ventilation and also help increase the load bearing surface area and improve the support under the mattress to prevent it from sagging into any wire gaps. It is also less expensive than the coir, but in the end, your choice would come down to your own personal value equation and what is important to you. All things equal, if sometimes in the future you’d like to upgrade the foundation and get a power base then I’d probably go with the coir rug.
Good luck with your multiple purchases!
I certainly appreciate your questions so that others can feel more confident that there are some good lower cost foundation options available.
Phoenix