I am sure you will hear this alot,(I am sure I am not the only one that does this) but as I am pretty crafty on the sewing machine (hehe), we buy on sale the mattress egg crate covers. You can get the twin size about 11.00 at Kmart or full usually about 15.00 on sale. I cut them to the sizes I want. double or triple the thickness depending on what they are for ( crate bottoms, or living room throw bed etc.) then use an old sheet (I buy lots of unmatched ones at the thrift store WAY cheap) run up a cover on the machine and voila! One custom bed with or with out arthritis bumpies! You can buy several different types of the egg crate foam.

Hope that helped.