Well there's a lot more to sonata form than just that, but in any case, the forms of the other two movements can really be whatever you want and doesn't have to conform the Fast, Slow, Fast model. This was more typical of the types of sonatas composed in the 18th and 19th centuries, and even then there was a plethora of options for a sonata. Typical forms for other movements include Theme and Variations form, Rondo form, Sonata-Rondo form, etc. You should take a look at some sonatas if even just to see how different composers utilize different forms. I would start off looking at some Mozart and Haydn and then work your way to Beethoven and beyond! Some suggestions I have for you are Mozart's Piano Sonata No. 5, No. 11, and No. 16, and Beethoven's Piano Sonata No. 8 and No. 15. These will definitely give you a good idea of the different forms that composers have used, and in the case of the Beethoven, the interesting ways they incorporate the forms. You don't really have to conform to these models though since these days there's not really a list of standards for composing a sonata, but they're a good starting point.