Teardrops n Tiny Travel Trailers

My idea is to use 4" foam for bench cushions for a dinette. The other purpose of these cushions are to be a mattress when the table is lowered in place. My wife needs a EXTRA FIRM mattress due to her back issues. I have checked out mattress toppers but the ones I find do not seem to be firm enough. I have about decided to go to a furniture upholstery company and see what they can do for me. Has anyone dealt with this or have any ideas?

Thanks,
Earnest

Pretty much anything you want on this site, http://www.thefoamfactory.com/

Thanks!