

You could add an SSD specifically to serve as a pagefile location and nothing else, in which case you could just get a small cheap one (a 32GB SSD would be more than enough for 16GB of RAM)
Honestly, assuming OP isn’t somewhere that the market for PC parts is extremely wonky compared to the US, if you’re going to get an SSD you might as well go ahead and get one big enough to serve as a boot drive. A 256gb SATA SSD is ~$20, and should be fine for that purpose. It probably won’t have DRAM at that price point, but realistically it’s not really necessary and still going to be a night and day upgrade over an HDD.
Reinstalling windows is hardly a laborious task most of the time, but even then my main point was that buying a 32GB SSD is pointless when you can get much larger ones for extremely cheap. Even if you don’t use it as a boot drive, more fast storage is never going to be a downside.