Hey length, .. while the other posters are correct that jelqs are a great addition to length gains (pre-fatiguing the tissues for easier remodelling in either direction) they're also a great addition ..obviously.. to girth gains -- and the other posters might not know about your
Enormous starting girth .. (of something like 6.5" iirc).
If you want to avoid bigger girth, I'd say be verrrrrry careful with jelquing and probably replace it entirely with heated warmups and massage .. and then do length-only exercises, and do a ton of time afterwards in a stretcher/
hanger/ADS of your choice ..
I'd additionally say to be careful of doing length exercises which hit the sides of the base: cranks, BTCs, LazyAss's, etc etc etc ..
I know that takes a ton of items out of the toolbox, but all of them can increase base girth and that translates into some shaft girth.
For the difficult -just- length, you're looking at straight pulls .. from the glans and from the middle, A-bends,
hanging .. maybe, (is "L.O.T." still a thing?), and healing time in stretchers/ADS.
$.02
Personally I got 80% or more of my girth gains concomitantly from doing general stuff. The length and girth just always went up at the same time and (minus experimenting with new stuff) neither one was anything I -had- to use separate effort for. Not everyone gets the same mileage, but if you gain girth easily ... well you named yourself Length for a reason.