Could anyone confirm, from a rather vague description, the correct
charger for:

A MacBook, bought new about 3 years ago (min 2 years, max 4 years), It's
got a retina screen and had an SSD fitted as an option at the time of
purchase. I'm not sure if it's a Pro or not.

I'm working from memory when I saw it last - it's for a friend in
hospital, and he can't be much help beyond knowing he's lost the charger.

I'm guessing/hoping it can be narrowed down to a 85W or 60W Magsafe 2 from

https://support.apple.com/en-us/HT201700

If it can be pinned down, what's the best place to buy one?

--
Cheers, Rob