Agree with this! Although you can get Windows 10 with Planet Coaster on a 64GB drive no problem you will start to run out of space rapidly. Once you've experienced SSD speeds you'll want more and more of your programs on it and suddenly 64gb and even 128gb fills up quickly! 240+GB is a nice size, it's not a massive step up in price from the 120GB models and is probably worth it in the long run considering the larger storage space will extend the useful life of the drive.
SSD's are probably one of the single best computer upgrades you can make for the price. I'm still using one of the first generation 64GB sata SSDs that I purchased over ten years ago now and although it's much slower than my other more modern SSD drives, it's still a lot faster than even a 2TB mechanical drive when used as a boot drive in the spare PC!
Some brands to consider: Samsung, Crucial, Intel, Toshiba, Sandisk, Kingston, Western Digital, Corsair, ADATA.
Thanks for the advice, I'm looking at a Sandisk as that seems to be the cheapest. I really do think that 120GB will be fine for me though, as I only will want to put Windows, Planet Coaster and probably Subnautica on there as these are the only games that take awhile to load. With Planet Coaster only at 7GB and Subnautica at 12GB, I don't think I really need anything bigger tbh. One more question I have though, is it a good idea to put Google Chrome on the SSD? I'm fine with how quick it is on my HDD anyway, but if it doesn't take up much space, I might as well move that too.