Not sure how useful this is but I assume somebody can make use of it.
https://www.notreble.com/buzz/2021/08/03/mitch-gallaghers-mix-tips-how-to-mix-bass-guitar/?utm_source=newsshowcase&utm_medium=discover&utm_campaign&utm_content
My Tech, in Stevenage, will make reasonable charges but getting parts for Markbass gear is a nightmare.
As @Bigwan says, it would be helpful to know what's wrong with it.
Let me be the first to congratulate you on a wise decision and offer my home to the bass should you need somebody to look after it indefinitely. 😉😉
Remember that I offered first!!
I'd suggest getting used to what you have currently before throwing sackfuls of money at instruments.
Playing fretless is not as simple as you'd think - I've owned several but always struggled. If it's your plan to then consider locking away all your fretted basses to avoid distraction.
If you're undecided on a J or P consider getting a P/J which will give you the best of both worlds.
Oh...and a harp...but a good one is thousands of pounds.
I blame @lawriemacmillan as much as anything. @Lozz196 and I went to one of his gigs - harp player in the band sounded amazing. Also I remember a Dub track from Glastonbury with drums/bass/ harp - blew my mind!!!
One of the dog walkers we walk with has a daughter who plays harp - one day I hope to jam with her.