Looking for suggestions on replacing boiler with a combi in an old house

Old house built in the 1960s.
I want to replace my system boiler with a combi to get instant hot water.
The plumber said I need a larger cold water tank, a pump, and new pipes. He said the old pipes cannot stand the water pressure.

If the pipes need to be replaced. Then the floor&wall&ceiling need to be cut to run the pipes.
If the floor/wall/ceiling gets cut, that means new flooring/ceiling/painting, why not insulation altogether....

A seemingly small thing could turn into a much bigger job.

I want to upgrade the place step by step
Is it possible to do one thing at a time?

Floors, walls, and ceilings can usually be patched to cover replaced pipes, particularly if you don't have any high-quality flooring that you'd want to retain long term.

When taking on a house of that vintage, it can be a good idea to work out all the changes and alterations you want to accomplish and get someone knowledgeable to advise on the best sequence, or what jobs should be done at the same time. For example, if you foresee layout changes or an extension down the line, make sure that's factored into any significant work on the heating system and where pipes are run.