Hey,
Dont know if anyone answered this before.

Aspen is totally fine, in fact lots of breeders use aspen because its really easy to clean. Only thing to be wary of is impaction - you typically want to avoid your snake eating any aspen. Also another thing to watch out for is over-misting. Someone on this forum told me aspen is prone to over-misting because of its low humidity, and if you mist it too often, your snake can get belly rot. As long as you fully replace the bedding a few times a year should be fine.. big bags like that of aspen are cheap anyways.

What I am using right now is a mix of ExoTerra Coco Husk (or Plantation Soil if I cant get coco-husk) mixed with ZooMed Forest Floor Cypress Mulch. Really does a great job with humidity for BP's. My humidity stays above 50% at all times, with no mistings. Fresh bedding will also raise your humidity 10-20% depending on how moist you make the coco husk. One thing to consider is if you're using Belly heat, so UTH or flexwatt, moist substrates tend to take much longer to heat up than dry ones. But eventually all moist substrates become dry after a week and heat transfer stops being an issue.

Hope this helped!