Try coconut shells. I buy them from the grocery store and break them in half. They work well, look natural, shouldn't effect your water quality and won't stand out in your tank like flower pots would. If you hope to breed them in the future, give them ahwile at the lower temp (good thinking by the way). After a month or so, start feeding them freeze dried krill and other meaty foods and raise the temp a little each day for a week. And have planty of caves for them too. Good luck with them and keep us posted.