Breastfeeding and conceiving

Hello all! My daughter is almost 21 months, after 3 years of trying we did IVF to have her. Ready to expand our family again but trying to avoid another round of IVF so I thought I'd start tracking again (fun fun). However, she still breastfeeds so my cycle is way off, 28 days one month, 36 the next. No idea when I'm actually ovulating! Any recommendations for good ovulation test strips, I remember using some before that weren't great. Any other advice?! Fertility appt 10/9, would love to conceive naturally before then, trying hard this week ;)