Congrats on your new Boa!
I prefer RHPs as well. But since Ultratherms don’t cost much I just went with both. Totally unnecessary since neither of my adult Boas rarely spend time in the warm areas.Because of this I keep the warm side 87-88.
Personally I don’t like Aspen. But you owe it to yourself and the snake to be open to trying different substrates to see which works best. Some people love Aspen.