Can anyone rec. a good basal thermometer?

Florence • Expecting baby #1 Dec 23!
Hey... I've sort of given up on trying to get useful info from tracking my BT b/c I feel like my thermometers are unreliable. I bought a new one recently and have no faith in it at all. Can anyone recommend a good basal thermometer that I can buy online that doesn't cost a fortune?
​Many thanks!