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 literally just finished Doomsday Book two days ago. The first 400 pages were kind of a slog, and I almost gave up several times. The last 150-200 pages were excellent and just flew by. I’ve been debating trying TSNOTD, (3 Men is one of my favorite books of all time) but have been hesitant about getting bogged down again. I will be rethinking it.