Several Short Sentences About Writing isn't so much a book that you 'read', more one that you peruse a section of every now and then. As such, I'm going to start Consolations by David Whyte.
That will technically be four books I'm reading at the same time (along with the Daily Stoic and Daily Thoreau) – maybe five if you include the audiobook of Oliver Burkeman's Four Thousand Weeks.
I've never really been one for having multiple books on the go but the nature of these means that I can dip in and out as required. I'm also looking for those serendipitous moments when things align across multiple texts and create connections that wouldn't normally appear.