I was having the same issue. Night time temps were getting into the upper 50's-low 60's. I bought a ceramic heater hoping that would be enough to control those night time lows. Although that did help some, the thermostat built into the heater doesn't seem precise enough to provide the temperature controls that I would like. After doing a small amount of research online, I came up with this:
https://www.amazon.com/gp/product/B01KEYDNKK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
It's relatively low cost. It has both a high and low temp control settings and should help greatly in controlling temps. I just ordered it about an hour ago. Plug fan into high temp control, plug heater into low temp control, set high and low parameters ... in theory this should work just fine!
I can report back once I have it in use. Item arrival expected mid week.