After my Acurite digital thermometer stopped working I looked for a decent replacement but that doesn't seem to exist. I looked at the standard floating Alcohol thermometer types but many reviews warned of low quality overall or problems with buoyancy (floating on its side).
How about a giant meat thermometer tweaked to float?
I bought the "CDN IRXL220 ProAccurate Insta-Read NSF Large Dial Professional" model from Amazon for $9.
The only tweak that was done to make it float was to attach a round piece of foam under the dial. At this point it's been floating in my pool for 6 weeks and no leaks. I did seal the calibration nut with silicone just to be sure and this also keeps the foam from coming loose.
I like that this thermometer can be read without removing it from the water. Mine tested to be pretty much dead accurate so no change was needed.