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We are right at the bottom of a hill and the reservoir is at the top so our pressure is currently very good
This sounds very promising.
In fact this is the case for my property... so yup, a power shower (the heater kind) is probably all you need. But if the pressure isn't sufficient then a cold water storage tank in the loft is going to be necessary... and if you add a cold water storage tank you want the head of the shower to be below the base of the tank... hence my "put the storage as high as you can".
If you don't need a storage tank it's because the outlet of the reservoir (the base of it) is higher than your loft. If that's not the case, introducing a storage tank eradicates the standard pressure, and now pressure is measured by the difference in heigh from the storage tank to the shower head.
If you can get away without a storage tank you're going to be great.
A plumber should be able to measure pressure and give you a good idea whether this will work based on the PSI of the pressure (they can calculate how high that will lift water and how much pressure will exist at that new height and the flow rate achieved... a typical shower head will still want 1.5bar pressure to feel adequately powered, 2bar is ideal... I suggested a 3bar negative head pump to push the water a single story high and retain over 2bar pressure at the shower head).
Time to speak to a plumber.
Velocio-
Those new accumulator (with a membrane or an actual pump) cold water storage tanks are ace. Mate got one as their incoming pressure and flow rate changes wildly through the day (fairly common I guess). Now they have 3.0 bar and 12-16l/m out of every tap and shower in the house, even with 2 taps on at the same time (or 1 big shower and 1 tap its still excellent). Didn't cost that much, basically a huge plastic sealed storage tank can be almost anywhere in house and a pump that goes on the side of it. Pump does make a noise, but can be programmed to only pump at times of day when your not at home, or at least not in the middle of the night!
'ACCU boost' is the brand, big grey silver plastic thing.
BrickMan
This is very useful, thanks!
We are right at the bottom of a hill and the reservoir is at the top so our pressure is currently very good (1st floor flat). So I was considering using a heated electric shower for an ensuite upstaris. Just a small combi and single shower at the mo. There should be space in the loft conversion for a small tank however.