https://www.dcurbanmom.com/jforum/posts/list/784285.page#14500104
Link to a thread about thermometers in this forum last year. There also was a more recent thread I think around March of this year. Search function shows thermometers have come up a lot on here over the years so you'll find a lot of recommendations.
Our pediatrician, who published a couple of articles about fever in children, always said something parents do not want to hear: Rectal temps are the most accurate temps for young children at home. Ear thermometers are loved by parents who hate to take temperatures but she said most ear thermometers available on the home market are not that great OR they're fine but parents just don't use them accurately on wiggly kids. She always recommended getting over any squeamishness about rectal temps, especially if you really think a young kid has a fever. Under the arm is just useless, as is forehead temp, unless you have one of the super professional ones like are being used for covid-related scans.
Be sure you get thermometer covers, and plenty of them, as well as a lot of first aid type alcohol wipe pads. Whether you're doing oral or rectal you will want both to cover and then clean thermometers. We use the CVS house brand thermometers and/or Braun thermometers (kid is much older now and we do all oral temps) and they have been fine. I always have two thermometers around so if I'm concerned about one reading I can do it again on another one.