Count another vote for bumblebee cats, aka akysis. MsJinxed sells them, that's where I got mine. Have kept them in substrates sized from fine sand to 1/4 in gravel and they have had no problems in any of these (really big, like 1 in, rocks might be a bit much.)
Only drawback is that they are quite reclusive and spend most of their time under whatever substrate you have, or else under rock/wood 'scaping materials. But when they come out to play they are hilarious as well as quite pretty. Nice little cleaner-uppers too. I would tell you to get 5 or 6 but I am planning on getting some more myself and last I checked MsJ was a bit low on supply.