i use reptibark but cuz the chunks insulate the heat beneath it, i just put a very thin layer of it on the warm side with some openings between the pieces to let the heat through. my girl actually moves it away when she's underneath the warm side hide box cuz she likes sitting on the bare surface.
if you do switch back to the cypress make sure it's not a blend. that stuff has cedar in it. i used it too until i found out theres cedar in pretty much all the cypress mulch at home depot & lowes.