"The industry standard"
The old mercury clinical thermometers were easy to use and accurate. Because of overblown fears about mercury you can no longer get these from reputable manufacturers. The Chinese versions are really not that good.
Tried a variety of the cheap electronic clinical thermometers. If they worked at all, they tended to give variable readings.
Tried an infra-red temple vein thermometer, which was not cheap, but seemed incapable of giving even close readings twice.
Eventually gave up, and bought the same thing used in hospitals and clinics across the world.
Decidedly not cheap, but fast, accurate and repeatable readings. The disposable sleeves are a plus when it comes to sterile practices.
If you care about your temperature readings being a bit more precise than alive/dead, this is the way to go.