I use a PalPens "Jumbo", it's 400x300x300 (you can see pics in some of the albums in my profile) I'll be keeping my Bredli in until they're a year or so old.
I use a 13W heatmat & a Microclimate 100 thermostat. I'm getting around 32C at the warm end, & whatever at the cool end (depends on temps in the room at the time, sometimes only 15C or so). Use a non-contact thermometer to accurately measure floor temps, don't rely on the thermostat guage (my guage says 27 yet I'm actually getting 32....go figure)