Not quite slim, but I've switched to a lower profile leather billfold made from the recycled leather of a BMW 740iL. You put your ass on it, so you know it's going to hold up well. The same company also does Air Canada and Alaska Air recycled material along with other cars. Rarer leathers like ones from the 993 cost more.
https://www.mariclaro.ca/collections...1996-bmw-740il