Showers, pumps and hot water systems

I'm looking at creating a new shower room. This will be in addition to the existing electric cold water fed one in the bathroom. The electric one obviously has flow and temperature stability limitations. I don't want to suffer the same in a customer built shower set up. My hot water system is pressurised. If I use a thermostatic mains pressure mixer setup, will I get a stable shower temperature without pumping or adding additional header tanks? I want a good flow and not to suffer variations when the loo flushes, washer is filling etc. The local plumbers merchant says no problem, but then they would wouldn't they?
Mark W.
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