I went straight into Hyginus and Caesar. Hyginus is not difficult at all. After LLPSI, you should be able to read this: https://www.thelatinlibrary.com/hyginus/hyginus5.shtml

Caesar is not too difficult either. The biggest problem I had with Caesar was that he used indirect speech a lot and LLPSI doesn't really prepare you too well for that, but you get used to it.