Opks.. When to use and which kind.

Megan • 25, Married to the love of my love! PJS 6/2/15 - CAS 10/20/16 ❤️Angel babies - EP 1/3/14 / MC 4/11
So I recently had a ruptured ectopic pregnancy on 1/3/14 & lost my baby at 6weeks and also lost my right tube & ovary. Currently me and DH are waiting on AF to start so we can start TTC again. I'm thinking of using opks this go around.. Can any of you ladies recommend a good brand? Should I get them offline?? Also, what CD do you start using them and for how long?? Help please!! :(