It makes sense that we don't find anything that belongs to Astarion in the palace. The spawn don't have anything and he's not someone who would keep a journal. I'm pretty sure the clothes he wears are all he owns.
I didn't think he'd have much, but I was at least expecting there to be some sewing tools since he knows how to do embroidery and how to maintain his clothes. He also experimented with making perfumes.
