Are you set on the 14500 size of battery's? You could do a 10amp Raptor or 10amp OKR, they will fit into a 1550P size box which is quite small with dual 18650's. I recommend this after building a 10amp raptor in a 1590G box, and then putting a SX350 in a 1550P. The 1550P is perfect size for on the go slips right in your pocket with a atty on. Parts for the okr and raptor will be about 45 bucks plus battery's, that does include a adjustable 510. Pics below are the 1550 natural and the 1590 black.
If you like what you see ill post a build sheet up so you can get parts orderd.
Good luck