Flow vs pressure for upstairs showers

bobfredbob

We’re thinking of putting a shower upstairs and looking for advice on what makes an adequate or good shower.

The previous owners removed the bath from the upstairs bathroom of a 1930s terrace house and moved it to a downstairs bathroom extension, leaving the upstairs bathroom with just a toilet and sink.

We have an electric shower downstairs which is very poor compared to the bath tap mixer shower running from the (very old, non-foam) hot water tank. I've used electric elsewhere and found it decent, so perhaps it's because we have lower pressure?

For upstairs, I've seen mixer showers (such as Mira Agile ERD) in diy shop for gravity at 0.1 bar 5.8lpm. But will such a low pressure mean the shower feels awful?

By contrast, 10.8kw electric shower says 6lpm at 1 bar. Would that feel better?

Fitting a combi would probably involve taking out kitchen cabinets to route the pipes and get a larger gas pipe; or moving it to a bedroom like the neighbours, but even the smallest combi would give a better shower due to the higher pressure?

I've thought about whole house pump such as the Stuart Turner Monsoon 2 bar, but am concerned about noise since the airing cupboard is in the bedroom next to the other bedroom. Is a pump likely to be quieter than a combi on full blast?

I've read about unvented cylinders. I'm slightly concerned about the ongoing cost of annual maintenance. Cylinder specs suggest they lose “<60w per day”, which seems very low (1/2p per day?) Does that mean water basically stays hot all day/week if not used? So any disadvantage to just getting the biggest cylinder that will fit?

I read that American showers are limited to 9lpm so guess I don't need more flow than that. But what about pressure and minimum flow? I'm not looking for a Commando 450, just something decent. We're (probably) not looking to use both showers simultaneously.

Thanks.