So i bought regular sheets, small s hooks, small diameter bungee line, and nylon strapping
I sewed the bottom sheet to the top sheet at the bottom, sewed nylon strapping in a loop design and placed them to the elastic part of the bottom sheets.(3 loops on each side of the fitted sheet, and two loops at the top and bottom of the fitted sheet). I then use the s hooks, and tie the bungee material to them, pull them tight from side to side and top to bottom. I now wake every morning with very well fitted sheets attached to my 4" mattresses. The top sheet never comes out (remember water bed sheets) because its attached to the bottom sheet, and the bottom sheet remains "quarter-bounce tight" at all times due to the bungee web keeping the fitted sheet from moving. Finally, i bought my sewing machine to do this, so it aint pretty, but it works great and you cant see my novice sewing job because everything sits under the mattress.
Hope this helps.