Either mat could potentially work with a r'stat. 88* is fine for basking, though you should try to get cool end / ambient temps up to 75* at very least. You could try sticking the larger heat mat on the other side of the cage, unhook the r'stat (if you say it's maxed out, it won't really matter), and use the larger heat mat on very low (with the r'stat) to heat the cool side, which will also end up raising the ambient temps. Then in the summer you could unplug the large heat mat and connect the r'stat to the smaller heat mat to cool things off.

Or you could buy a low wattage halogen bulb to have on during the day (your current temps are fine for nighttime), or a CHE to keep on 24/7. I have never had luck with bulbs in glass cages, especially CHE's (humidity drops to 10% and stays there), but feel free to experiment. Keep trying things; eventually you'll find something that works for you.