Originally Posted by RefRick

I am debating between 42 and 44, but I think 42 should be sufficient. I am not an elite athlete or anything, just a guy in decent shape who rides a lot. Plus if I get it wrong, I am confident I will be able to sell off the extra part.

Are you running GRX components as well or do we just have the same gearing? I have been window shopping since cxwrench replied. So far, I have found 2 companies that make replacements specifically for the GRX series: Wolf Tooth and Garbaruk. Both are also compatible with the 600 or 800 series.
Shimano only makes the GRX in 40t or 42t. I have not checked on chainring compatibility with other Shimano series.
Wolf Tooth offers 38t through 46t but the only size they have in stock is the 40t on their site. Looks like JensenUSA might have multiple sizes in stock.
Garbaruk offers 38t through 52t.