I have same problem although I have a chair I want one lower because my hot water runs out quick on the bath. seen a couple on eBay this AM but not sure yet as Ive not looked properly.
Im just about to bath her and Im going to put a towel in the bath folded at the top like a pillow - then I have a wash to go on anyway you see so in the towel willl go with that
Sponges aren't meant to be great but then again Im not sure how or if they can be washed because I'd easily give a quick was on one of those (if it can be) therefore it will be clean for next use & not soaked with dirty water. Been thinking about this too.