My Boiler is on its last legs - had our annual service today and the British Gas Crook, sorry, Man said spare parts were no longer available etc etc

So I'm preparing for the worst. We currently have a vented(?) system - cold water tank in the loft and hot water cylinder in the Airing cupboard upstairs. Boiler itself is downstairs in the kitchen. We have an ensuite with a Shower cubicle - thermostatic shower valve fed by an Aqualisa pump from a hot and cold feed from cylinder/cold tank.
In the main bathroom, I have a power shower fed form the same hot and cold tanks.

Seems as if opinion is certainly skewed towards Combi systems - question (finally) is....will I need to replace my Showers (v v problematic) or can they run with a new combi system or similar. I'd plan to do as much DIY as poss - prep work and flushing etc etc - what do people think I should do?

Very grateful as ever

Alex