showers from combi, are, by and
large, superb.

Didn't work for me. Whenever there was any cold water demand the pressure
dropped enough to trip out the boiler so (with a long-ish pipe run) there
was an unacceptable wait for more hot water.

You could check this for yourself by running the bath hot tap and seeing
what happens when someone flushes the loo.

I bit the bullet and put in a tank above the shower, with a power shower.
Your alternative might be a high rating electric shower (but expect it to
need rewiring).