Though if I’m understanding the OP correctly he’s not particularly bothered about performance, simply about keeping the computer running now Vista is out of support (it’s been unsupported for almost 5 months, it’s about time!) The correct answer has been given already – I expect most computers running Vista will run W10, though clearly not all. If the OP did have an unsupported computer W7 would be the alternative option, though that’s only putting the problem off for a couple of years.
Whilst I get the love for SSDs, I’ve just put a new 500GB hybrid drive in mine for the W10 upgrade. Hopefully I’ll get most of the performance benefit without the huge cost of an SSD that size (which I do really need, old disk was 250GB and almost full – yeah I know I should be putting stuff on the cloud, but a lot of that was stuff which I can’t easily do that with). Don’t want to spend huge amounts on an oldish computer – though presumably newer than the OPs as it was running W7 originally, and the 500GB hybrid is still cheaper than a 120GB SSD which really wouldn’t be big enough for my use given current levels of software bloat and the stuff I do – I’ve already used 80GB without really having any data on it.
Anyway the performance improvement is significant so far, though I don’t know how much of that is down to the hybrid drive and how much to replacing an old bloated W7 install with fresh new W10 (it’s running noticeably cooler, so I suspect at least partly the latter).