The Thomastik Flatwounds will be a major improvement over the dull monel strings as they are flatwounds that sound more opened than anything else in this category, but if you're looking for harmonics, you'll have to go roundwounds.
If you have a bit of patience, as they need to break in and it takes some time, try the Rotosound's RS66LD, they have all you're after.
That said the Labella White Nylon's are the best nylon strings for fretless as they don't sound plastic like all the other proposals in the nylon range (and they are roundwound inside the nylon).
You could also try the Elixir nickel plated and of course coated as they won't mark the fingerboard and sound excellent on fretless basses.
That said start unplugged with the strings and once you've found what you like, let the thunder get alive.