Cool what jazz bass do you have and like? Let’s start with that.
I have a few short scales the Mustang feels great and sound awesomely retro just love it and the sterling SS is decidedly Stingray but with a bit thumpier. The 30” and 32” scale Jaguar is fun as well. Best feeling to me is the SS stingray, but the Mustang offer the best retro feel especially if you are into P bass.
I took a chance on them, never heard of them, but my first one only cost me
$102 USD plus shipping from Germany.
They sound ok, don’t hurt my messed up shoulder.
I don’t care much for the p bass sound when it’s just me noodling around by myself. Plus the larger frets near the headstock causes issues with my fretting hand. I broke some fingers several years ago, didn’t heal properly and sometimes do weird things when I spread them like locking up.
I’ve done a few neck swap but usually to the same brand of instrument. Your bass most likely have a different neck pocket size. If it’s close you can sand your way to fit it.
More important is the length or effective length of the replacement neck measure from nut to bridge. It should be close to your original 30.3” scale. You do have some wiggle room but not much, too short or too long you’d suffer with the intonation.
It’s definitely cheaper to shop for another and keep the Gretsch as is. You know taste changes back and forth all the time sometimes you want narrow sometimes you want wide string spacing. I can understand in your case it’s more actual physical limitations.
Check out the Squier mini bass, they are almost the same size as the guitar and the neck is quite comfortable, compact and fast.
Mmmm, find a Bass with the neck you want will be a better idea, for me changing the neck is more difficilt than you think, you will need to respect the distance between the nut and the bridge and sometime you need to move the bridge backor front and it will change your intonation.
Best answer, and the Squier mini have a really slim and good neck, I have one and I love it.
Changing a neck can be really tricky on a different brand, you need to know what you are doing, easy to think it’s easy but you need to respect a lot of rules and be handy and at the end you can ruin your original bass.