The question is: will you move Steam to the SSD? If yes, then get the big one. If not, your OS, office, messengers, browsers will fit on the smaller SSD without any hassles. Then you can use your old HDD for Steam and storage.
I know you did not ask this, but I would recommend keeping steam on hard drive bc SSD really does not make a difference in gaming performance outside of cutting levels' loading time by 40-60%. If it bothers you THAT much then sure, use SSD for games.