Is your hot water system, an open vented system, or a combi boile
My bad, sorry 3 storey townhouse.You say 2 storey townhouse, do you mean 3 storey??
A 2 storey property shouldn't have issues for water pressure on the first floor.
If you are confident and competent enough, you can always buy a new electric shower try it. If problem persists then it's definitely water pressure issue.
Is there an electric shower brand/model you recommend?