Upgrade of relatively new CSU?

Very much doubt it on a property that age. Get a registered electrician in to quote you. I’m surprised you have no spare ways on the con unit though if it was built in 2017?

Get an additional CU fitted alongside your existing just to house the circuit you want. Will be alot cheaper. Put an ad on here asking for new 6 way CU to contain x 1 new circuit.

It’s quite straight forward to change a consumer unit - there should be virtually no mess and certainly no walls to be damaged

There should ideal be enough room around a CU to allow the replacement of a slightly bigger one ( bigger in terms of physical size of the box ). You could however “make space” by replacing the existing consumer unit with one of very similar dimensions by using a CU with all RCBOs fitted. How does this make space? Well more than likely the existing box has circuits ( banks of MCBs ) spilt between 2 RCDs, each RCDs will take up 2 spaces each, RBCOs combine MCB and RCD function in one space, so you can change like for like for existing circuits and make space for 4 new circuits. In theory. Price wise a 10 way box is £100-£150, RBCOs are £30 each ( cf. £4 per MCB ). So RCBOs are more expensive but you’re investing in the best and more future proof hardware. This might also make space for surge protection. This typically uses a 2 space gap and add maybe another £50-£100 but it protects your installation ( wiring, connected devices, computers, smart devices etc ) from voltage surge which could be many more times costly to replace than the initial outlay. This is only half the story though as the electrician you use will want to know why you need an extra circuit and what it’s intended use is. If it’s for a low power application then not that much of an issue, if it’s to power 2 11kw EV chargers then you’ll be running into issues of maximum demand on the supply head ( the cable and big fuse that supplies your property ). Eg a new load of that size could exceed your existing electrical infrastructure.