My pick would have to be the A Whole Nother Story trilogy, in which (spoiler warning) you can only travel back in time. But because time is in a loop of sorts, if you go before the beginning of time, you will be at the end of time. From there you can go back to any time you want to. And time paradoxes cannot be produced. Plus, your memories from the previous timeline exist as well as the memories from the new one.
I’m sad the author died because I would love to read a sequel.
Talking to book dealer a while back, who said he’d spoken with Kens wife and that there was, in rough form, a sequel but he passed before he could finish it.