Honestly, those slap-on plastic thermometers are fine (the ribbon-thin ones that look like a rainbow and are only a mm thick or so). I know I was kind of lackadaisical about a hydrometer, earlier, but a cheap-ass thermometer is actually less important than a good hydrometer.
You can just stick one of those thermometers on the side of the carboy (sparge or post-sparge). It gives you “good-enough” info. A decent but still pretty generic candy thermometer gives you “good-enough” temperature readings during the boil and mash.
The thermometer tells you when you’re ready for the next “RIGHT-NOW!” step when everything is hot, but the hydrometer tells you when your ready for the next “oh, heck, I should call some friends and my cousin for Thursday!”
I do know what you’re saying, I’m sorry if this doesn’t directly address your response, the most Funkiest of Jems. (@FunkJem, for anyone who didn’t catch that. Seriously…)
It’s both art and science, no one really knows how to do it totally right, and we’ll always screw it up (except for when we don’t, and then it’s amazing!)