With greatly variating room temps a dimmer is not likely to work well you will still get wildly variable temps. All a dimmer does is cut the power to the unit so if you set it to 50% power and everything is correct with a room temp of 78º but then drops ten degrees over night the hot spot will also drop ten degrees. In that situation you need a thermostat there are many on the market but I'd say a ranco or johnson is the cheapest I'd call acceptable (avoid zoo med 500r) and personally if you can buy a proportional one like a Helix or Herpstat they are most $$ (around 110$) but are rock solid and will serve you if you have one snake or 21 snakes you will keep using it.

Welcome and yes heating can be a challenge, and everybody has different problems and situations you need to find a solution for your flavour. The P-T-stats are the most flex-able.