I have done some reading that BF makes temperatures lower. I've been noticing it in my own chart as well. Some of my temps are close to 96F and the temps actually seem lower the more my baby nurses during the previous day. Mine are ranging from 96.1 to 97.4 though not staying in any range for more than 3 days.
I wonder if I can get more than 3 temperatures in a similar range in a row I might actually ovulate. My old coverline was 97.5 at it's lowest, and generally above 98 after ovulation. But it makes sense that the thermal shift would be lower because all the hormones are fighting and luteal phase defect, signs of which are low thermal shifts and short luteal phases, is common in BF mothers.
I thought this was interesting
https://www.bellytales.com/2006/03/06/ovulation-duing-lactation/