I use a CHE with a thermostat but you can get a cheap lutron (brand name) dimmer switch to control the temp of a CHE to get the cool side and ambient temps to where you want it. Dimmer works but you need to measure the temperature of the substrate below the CHE to dial in the dimmer to where you need it.

Dimmer example (you can get them at home improvement stores)

https://www.amazon.com/Lutron-TT-300.../dp/B0000BYEF6