I highly recommend the 3M Nexcare basal thermometer, simply because it has a backlight! I hate all the others because I have to move to reach for and find my cell phone to shine a light on the thermometer to make sure it's turned on a ready to go, and I feel like that may mess up my temps from moving too much. It's also a pain! So I bought this one:
https://www.amazon.com/BD-524560-Di...1&sr=1-2&keywords=basal+thermometer+backlight
and I love it! It also beeps every few seconds to let you know it's working and taking your temp accurately (letting you know it's in the right spot, etc) so I like that also because I don't have to wonder the whole time if it's even on and working.
Hope this helps! Good luck!