Open-ended book selection produces a long thread, a tied vote, and a delayed meeting. The fix is to narrow the field before anyone starts campaigning.
Constrain first, vote second
Agree a page cap and a rough category before nominations open. “Under 350 pages, published this century, not something two of us have already read” eliminates most of the argument in advance.
Nominate in a fixed window
Two days. Three nominations maximum. Anything longer and the enthusiasm has already leaked out of it.
Let the host break ties
A rotating host with a casting vote is faster and fairer than a runoff. It also gives every member one month where they get the book they wanted.
Keep a bench
Runners-up go on a list. Next month you start from the bench rather than from nothing, which turns a recurring debate into a queue.