Booster pump recommendation needed

Hi. We have a summer cottage supplied by a gravity fed spring. We need a booster pump to slightly increase the pressure in the shower. It basically dribbles out water now. I'm saying "slightly" because I don't think the system can handle a high powered pump due to the limited flow from the spring. The spring feeds, in order, a toilet, water heater, kitchen sink, shower and bathroom sink. Only the shower is a problem. I appreciate any help.

Ideally, the spring feeds a poly tank, and the pressure pump is fed from that. The pump, then feeds a pressure tank, and your system.

Yeah if your spring cannot supply enough for a booster pump, you need a storage tank like this one.