Pathfinder 2e Character Discussion

I'm playing a starlit span magus in Kingmaker, and I'm considering getting a staff in order to augment my spell list. But I'm having trouble deciding which staff I should go for. I have Trick Magic Item, so I could go after staves of other traditions if it makes sense.

I'm also looking at Fused Staff to manage my bulk, but I'm not sure the action economy around it is sound when put with Spellstrike action economy. Anyone have experience with this feat?