Towel, or get a bidet with an air drying option (but few models have effective dryers, so shop carefully).

I have yet to find a comparison of embedded energy costs between bidet dryers and a supply of cotton towels, but I wager towels will win out when taking into account bidets breaking down. As far as I can tell, they're very repair-hostile designs, and would love to find a manufacturer that stocks all the parts for their models for a long time.

I waited for a long time because I thought I needed an outlet to plug it in (for warm water), but it turns out that cold water is totally fine. So you just attach it to the existing valve right next to the toilet. It's fairly easy and not expensive (< $100)