If you want to replace the second bass, check first the string spacing. Like you I switch between the two, my fretted has the classic 19mm string spacing, mt fretless Spector only has 16.5. I’ve got used to it so I’m not replacing either at present but just for a short while when going from one to the other it feels different and I am conscious that I might just play the wrong string or hit two at once. I believe the Ibanez basses have close together string spacing ( but I’m sure others here can confirm/deny). There are quite a few bass collection basses coming up for sale here and elsewhere, why not get one and defret that if there is t a fretless one around already then everything will be the same! 🤩