An under tank heater and a reliable thermostat are your best bets. Basking lights and ceramic heat emitters totally suck humidity out of the air. Balls need around 50% humidity all the time. Thermostats that come highly recommended are Johnson controls, ranco, herpstat, helix and sypder robotics.
Personally, i'd get a real thermostat and be happy and stay away from rheostats and stuff like zoomed repti-temp 500Rs. Those are only really good if your room temps NEVER fluctuate. There are people on this site that use them with success, but I could never get a rheostat type thing to work for me without hourly adjustment.