Mickster wrote:

The water from the shower comes out very slow even when turned on at
full power, it is a mixer type system and the water tank is in the
attic.

What can i do to improve the pressure?

Either raise the water tank in the loft on substantial stilts to provide
extra head, fit a (twin impellor?) shower pump near base of hot water
tank, or get shower replaced with electric power shower fed only on cold
water from rising main.

A different nozzle probably won't make much difference, it'll still feel
like standing under a couple of dribbly Jif Lemons ;-)