Here is a link to the one I bought last year.
It's $12.98 on Amazon, free two day shipping if you have PRIME.
Doesn't have a thermostat, but I used it without any problems overheating, just watched as the soil or growing medium dries out quicker.
I placed my seed tray with the starter cups directly on it, and an overhead T-5 light above. It really worked a trick to get them to sprout quickly.
https://www.amazon.com/certified-See...=seed+heat+mat