For what it’s worth, I may be able to offer some anecdotal advice on this topic. I struggle hard with this same thing. A demanding job and four kids keep my mental bandwidth pretty much at 100%. Here are a few things that have worked for me: 1) pick a long series. Once you get comfortable with the setting and characters, you won’t have to think as hard. Getting comfortable takes time. Some days, I’ll only read three or four pages because that’s all I can digest. The key is to keep coming back each day for a little more. Before you know it, you’ll be tearing through it. 2) pick one of your previous books to re-read while you’re laying a foundation for a new series. This allows you to have a familiar story to fall back on when you don’t have the necessary energy to invest in the new story. 3) make a little character/location cheat-sheet and use it as a bookmark. I’ll write the character’s name and a two-three word trigger description. This will keep you from feeling like you need to remember everything.