Swmbo has briefly mentioned during conversations over the past year or so that she misses the Wii fit she used to have a few years ago as she used to use it for exercise. I've toyed with the idea of buying one but looks to be outdated now. What would be the best option of buying one or something similar?

If you have a Wii U you can use the older Wii version or the newer Wii Fit U version. IIRC we have a Wii U but the vanilla Wii game and balance board.

https://www.amazon.co.uk/Nintendo-Meter-Green-Balance-Board/dp/B00B8QDNN6

We have no console (apart from my PS3 which is in the garage). It was basically a toss up between a PS4 (because Crash Bandicoot has been re-released and wife loved it when younger) and a Wii (because swmbo loved the old Wii fit). But as I've since found out, Wii U was discontinued in January this year. The other option would be to see if there's a version for the Nintendo Switch but don't think that'll happen before Xmas.

I imagine there are cheap pre-owned Wii Us aplenty in CEX, Game, etc. I still like mine (technically the kids) and play Mario 3D Land, Zelda BOTW and Mario Kart.