Today’s rectal thermometers look like they do, partly because that is what a quick silver thermometer must look like due to physical limitations.

I suggest making it more user friendly.

First get rid of the long scale. It is not used in today’s electronic world, so exchange it for semi circular wedged form; like an orange clove. Easy to position between the but cheeks, and unless you are very very voluminous, easy to find again.

The temperature sensing part must not be sharp in any way. Not even with angles. Make a smal bulb and position it on a adequately long semi rigid stick. Mount this stick in the middle of the wedge, where the orange’s seeds should be. Easy to insert, easy to retrieve.
Now you have the insertable protrusion of a good length to insert. Not too far, not too short.

When you start the oven it goes into a warm-up phase.  When the right temperature is reached a light turns off.  It means I have to watch that light once in a while to see if the oven is warm enough.

Why not let there be a small chime when the temperature is reached.

Not an electronic beep because there are already so many irritating sounds around us.  Just a nice little chime please.