Rocky Mountain Mattress Company. They made my new mattresses when I converted from crosswise queen to twins. I sent them a paper template for the curve at the head and they fit great. Do a search on the web for them.
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2013 Silverado 2500HD Duramax/Allison LTZ
WBCCI #9632, TAC TX-10
If price is an issue, memory foam and other foam (such as the 99 dollar very comfortable Ikea mattresses) cut very nicely with an electric knife-- simply peel back the cloth layer, cut the foam according to the paper template you made, and put the cloth back, sewing around the new profile.