A thermostat is literally the MOST IMPORTANT piece of equipment you can have. Not using one you are risking heat spikes that can cause serious burns, neurological issues and even death.
Your temps may be spiking without you even realizing it. A thermostat would eliminate that problem since it not only KEEPS YOUR ANIMAL SAFE, it also regulates temps so they don't fluctuate.
Not having a hygrometer also makes no sense, EVERY care sheet ever has humidity requirements on it. Why? Because humidity is IMPORTANT.