Sometimes frustrating things lead you to useful things. On the website of the publisher of the textbook that was annoying me so much, I found some links to online resources for physics. One of these was Science Joy Wagon, which provides both online physics lessons (most by subscription but it is only $5 a year for a single user) and physics workbooks (2 versions, with or without trigonometry). The workbooks are $30 and come as a PDF file with permission to print up to 200 copies for your students (which means you could use one for teaching a co-op class). The workbook includes labs and problem sheets. Just what I needed — someone else to write those for me. Hurray!
I think I now have enough planning done to be able to get started. Or at least to leave it until we are actually going to get started. That might be June, but maybe not until the fall. I bought the workbook (with trigonometry; Tigger likes that kind of thing) and might consider the subscription in the fall.
BTW, as I find different resources, either from things folks say in the comments or from my own searches, I often add them to the Useful Homeschooling Links page. That page is categorized by subject and I’ve put comments next to things (as much to remind myself as anything). Feel free to check it when you are doing your own planning.