If you loved the first Mistborn trilogy, you can’t really go wrong with any of Sanderson’s other works, really. A logical step would be the second Mistborn trilogy, which can stand on its own, but you’ll definitely enjoy having just read the first one, having that universe fresh in your mind. But if you don’t feel like hoping into another large undertaking, there’s lots to read, such as The Emperor’s Soul, the Legion novellas, the Reckoners (which is also a series, but perhaps a bit lighter in terms of concepts, very action-oriented. Then, of course, there’s the Stormlight Archives, his most extensive work, which is truly epic and definitely worth the read. Plenty of other stuff still, the man is a writing machine! Enjoy discovering these, I wish I could read them all again for the first time!