A couple of things to help you decide:
- Gauge: you say you're used to 45-105. You can get that with the La Bella DTF Standard set (45 65 85 105), but the Thomastik Jazz Flats only come in 43 56 70 100.
- Tension and stiffness: given those 2 sets, the La Bella will have a higher tension. And, unless you go to their light tension set, the La Bellas will be much stiffer feeling than the Thomastik.
If you really hate loose feeling strings, Thomastiks might not be for you.
- Tone: main difference, to me, is that the La Bellas would be the classical thumping flats, whereas the Thomastiks tend to have a more woody and focused sound.
La Bellas are moore boomy/fundamental/raw; Thomastiks are quite more harmonic/mid-rangey (this is how I hear them after trying both in several basses).
Also, on a fretless, both will go "dead" eventually, so they aren't the most "mwah' friendly strings. I've found that the Thomastiks give a bit more of mwah or "singing/ringing" tone, on a fretless.
- Flats on a Jazz: lastly, after having tried many brands of flatwounds on several types of basses, I've found that, for my taste, Thomastiks are the ones that suit Jazz basses the best.
I like both Thomastiks and La Bellas on Ps, but on Js, I've found that the more "focused" sound of the Thomastiks is a better fitting.
I find La Bellas on J a bit too "burpy/open" sounding, while the Thomastik give me a much more articulated and defined sound, specially in a mix.
Hope this helps you a bit