I went down the rabbit hole on historical instruments, something that I haven't paid too much attention to, and found out about the violone and lutes, especially how the frets on these instruments are basically just gut string that is tied around the neck. Long story short, I got some 0.7mm nylon string and it works perfectly fine without any modifications to my bass. I'm not suggesting that this is a serious endeavor but it's really fun to play your upright as if it was a fretted bass guitar and at 3 bucks and half an hour of fiddling around with some string it's just plain fun without any real investment. Maybe this is old news but I just found out about it and I think it's really neat.
I support anything you can do to get more people playing the upright bass. In time you'll likely enjoy the tradition of no frets. For now, have fun but get ready for endless abuse from the uptight crusty crusty old grumpy "my way is the only way" old white guy geezers around here....!!!
You can't play it as if it were a bass guitar, because the fingerings will be necessarily different. If this helps you, okay, but I strongly recommend that you still study proper db fingerings.
Since the early instruments would be gut strings and gut frets, to be a modernly-historically-correct you need synthetic gut nylon strings instead of steel. (I'm mostly kidding). Does the "fret" have a tonal influence? This might be a viable alternative to gut for early music performers who strive for period accuracy in gut unfriendly environments.
Maybe I should have made this more clear, I play (or rather learn) upright bass normally. This was just a fun little project that came to mind so I did it (again, barely any time or money invested, completely reversible, etc.). And since I learned bass guitar with a 124 method of fingering anyway it's actually quite similar for me. This isn't a shortcut to get good intonation or an alternative, just something to have fun basically. And it is fun, you can basically play "out of your league" because you don't have to be careful about your intonation. Obviously I can't compare it to gut frets because I don't have any at hand, but the sound is actually dampened and a bit more quiet than without the frets. Makes sense, the nylon is softer than the ebony which the string is usually pressed against. The tonal characteristic also changes since there is no sizzle or "mwah" that you usually have on a fretless instrument (and my bass is set up with a fairly low action).
On my first double bass I have installed nylon frets. One reason was coming from guitar and viola da gamba and the other that there were holes under the fingerboard run the nylon through so nothing running over the back of the fingerboard. It was nice to be able to play in tune quickly, but when I made the transition to fretless, it was hard to get rid of the imprecise intonation that occurred to being used to halftone quantizing by the frets. Also the nut needs to be high enough (probably higher than a usual low nut) or the nylon fret low enough (which might be too low with a low nut) to let enough room for vibration. My frets couldn't slip due to the holes limiting slippage, but the frets around the neck can, specially when using using a very smooth material like nylon. For classical music frets might be OK, but for jazz and maybe also folk music some bending or glissando wouldn't work or sound different. It depends what you want to do. Frets might help if you work mainly on the bow first until you feel good using the bow (well, who really does ...) and then work on the intonation without frets (not needing to think about the bow), but I think in most cases the intonation goes hand in hand with the bow.
I'm wondering now if the nut on my bass is a tad too high. A business card slid under the strings gets stuck when approaching the nut, so I thought that was a fine action at the nut. I'll mention it when I get the bass checked out by a luthier at some point to finetune it. As for the frets slipping, they really don't. I tied them higher up and slid them down so they get stretched and hold on fairly tight. However it is true that the nylon around the neck hinders playing ability somewhat. You certainly can't slide your hand up and down the neck easily.
I would think the hardest part would be running your hand over the back of the neck easily, and without dislodging the frets. But go for it. Like any other reversible mod, you have nothing to lose.
I would get some simple Viola Da Gamba solos to work on with them. It will get you the right sound, minus the gut strings and period bow, of course. Yorke has some.