I just want to cosign the general opinion that it is really worth it to go through the (sometimes) rather odd process of contacting Bob at Pro Products. I recently got an RHP from them and the production time was a little slow. In the email apologizing for the slow response he said they were overwhelmed with lots of orders that were being slowed down thanks to materials shipping issues related to COVID.
But unless you really must get an RHP as quickly as possible, it is well worth the wait to get ProProducts. Just be sure to let them know what type and size of enclosure you're dealing with, the ambient temperature range in the room the snake will be kept in, and what type of snake it is (this is the info he's asked me for when I've ordered from him). He'll then give you a specific recommendation of what to order as well as instructions about how to order.
If you don't want to call, email again and be patient; I think they are getting hammered right now.
As others have mentioned, the ordering process is a little weird: Just order something random off of their website, then in the 'comments' section let them know that you DO NOT want to order that thing, and you actually want to order an RHP - then add the specific size/wattage he recommends. But he'll send instructions for all that when he provides his recommendation.
Side note: Apparently he's kept Green Tree Pythons for a couple of decades. When I ordered an RHP for my GTP, I got a two-page email from him discussing enlosures/heat/light for GTP. It was unexpected and quite cool.
You asked about thermostats. Since it's for just one enclosure, you could look into the Herpstat 1 Basic. It's an outstanding thermostat, and will last for years.