basal thermometer recommendations?

Sorry I know this has been posted before by others but I thought it was worth asking again.

I just got my period, which concludes 5 months of trying with no success for our first. On to month 6. I quit doing opk’s after the second month but I’m considering starting them again. I’ve never charted my bbt but I’m thinking of starting that this month. I wanted to be as relaxed as possible, but I’m just wondering in case there is a fertility issue, maybe it would be good to collect that info for medical use later?

I’m 30, my husband is 37. We have a couple risk factors between us but I’m still “below the age of 35.”

He had bladder cancer a few years ago, and in my early 20s I had chlamydia at one point but it was caught really quickly. We are otherwise healthy adults. I have regular 27 day cycles but I suspect I might ovulate later in my cycle and have a short luteal phase.

Anyway, sorry that’s my history. What thermometer does everyone use? I’m looking at getting one.