The Nissan Path

I am looking to replace audio for my 06 pathy. looking for suggestions. something which doesnt occupy any space as i need to use my third row. i have the base mode headunit with speakers. not sure if replacing the door speakers will make any differen but definitely replacing the head unit with a double din to have a backup camera installed.
any suggestions on subs ?
is it worth replacing the door speakers ? if so which brand.

i was looking to replace all the door speakers with bose so that i dont have to get a subs.

thanks for all the inputs.
KB

Base system audio speakers are likely 4 ohm. Bose door speakers are 2 ohm. You would better off just going with a good set of aftermarket speakers than going with Bose speakers. You should check out Crutchfield.com. Prices are fair, great selection and they give you the installation kit, instructions and harness adapters when you buy from them. Their service is excellent, as well