Yeah, you can go to smalls. Most male BPs never need anything larger than a small. My males are both a little under 1400 grams and get a small every 10-14 days.

Also, you mentioned the substrate temp, you actually want to measure the actual enclosure surface since your BP will push substrate around and end up on the actual surface.

You mentioned you have a rack on the way, do you already have other snakes? If so, are you following a strict quarantine?