Not sure if OP is still around. Some basic suggestions:
Don't buy a name brand mattress. They are only one-sided due to private equity owners realizing they could shorten the life of them by (a) sewing in a mattress topper that would die sooner (b) only including one side.
I'd suggest going with a natural Talalay latex mattress from a local latex manufacturer. They basically cut it to size.
Alternatively, you can order Sleep Innovations on Amazon which is basically a...