Best digital thermometer for tracking?

[CatnipMouse]

Hello hello! I usually hang out on the Infertility board but have popped over here to ask you all for recommendations.

I've got a couple of months to wait before my next IVF cycle so it's back to old fashioned (and probably pointless) shagging for a while. I have tried to track my temperature in the past to spot ovulation but it's never worked that well. I think perhaps the cheapy thermometer I used is not up to the job, it seems to rely largely on some kind of random number generating function. The ovulation predictor sticks seem to work for me but I'd like to use both approaches together.

So is there anyone who gets on well with temperature tracking and what thermometer would you recommend? Thank you for any tips!