I recently picked up a Sire Marcus Miller V7 2nd Generation 4-string Fretless.... I'm looking to get much more 'mwah' from it that I seem to be able to now...I've been advised to get DR Sunbeams. Does that sound right?
Sunbeams were my fretless go-to for a long time; great strings!
But the most recent time I bought a fretless, it came with D'Addario XT coated roundwounds.
I removed them to install a set of Sunbeams and actually found that I preferred the D'Addarios, so I put them back on.
As others have said, low action and minimal relief are the keys to "mwah".
The more prominent mids and (to a lesser extent) highs in roundwound strings are another key to that vocal "mwah" tone.
Yes, roundwound strings will leave
visible marks on the fingerboard - but generally, those marks are only cosmetic, not actual damage.
The biggest technique difference affecting damage/no-damage is how you do your vibrato:
On a fretted bass, your vibrato comes from moving your fretting hand parallel to the
fret.
On a fretless, that vibrato should come from moving your fretting hand parallel to the
string.