Replacement boiler instead of one I have at the moment

Yes you'll need a bit of plumbing alteration. Alternatively you can replace your old cylinder with an un-vented cylinder and keep your existing boiler.

This does require a reconfiguration, it all depends on the existing system and if it’s fit to be ‘converted’ or if the hot/cold needs re-piping, in short either way X amount of pipework would be required no matter what, which unfortunately would mean floorsboards up ect, it’s best to update pipework when upgrading to a combi system as their is always the possibly that the old(unpressurised) pipework leaks when swapped over to a pressurised.

you should first check your main can supply your needs to have a combi boiler.