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.
That book has some of the most poetic descriptions of the love of science and math in it. I remember that the most. I’m usually pretty frustrated with how stupid and formulaic time travel is in stories, but his conception was so unique and really poignant. I was not expecting to cry and feel so much when I picked it up.