What length laces do I need for 10 sets of eyelets

My Sorel boots have 8 sets of eyelets and the 72" laces I bought were a bit too long, which I don't mind at all. I would get this same 72" set of laces for your 10 eyelet boots.

How thick or what diameter are these?

4-5mm or 3/16”. A little snug for Rocky speed laces, but they work.

The laces I got for my husband broke. How do we go about getting a replacement?

You should ask to the costumer service! If you wanna ask for a replacement or refund for any defect of your item. I have no complain about mine! Because they are fine.

Do these work with sperry rain boots?

I am not familiar with Sperry rain boots but I can tell you that these are very thick shoelaces. I purchased them for sneakers but I think they would work better in boots.