Bookshelfs budget is $ 2000.

Second the Vapor Breeze. Best audio purchase I have made.
Compares to speakers costing twice as much.

FWIW I just took delivery of a pair of Wharfdale Dentons from Music Direct - cost $499 delivered. I've set them up with a 40wt tubed amp, 3 feet out from a back wall and 2 feet from side walls and I'm impressed! Warm with detail and excellent bass (considering their size). I'm really enjoying them. (They are not replacing my main speakers though, just used in a second system.)

Another vote for Vapor Breeze. Another option at the upper end of your range is the Fritz Carbon 7.

I am a big fan of the Vapor speakers' sound (my faves are the Aurora and Nimbus, but I have also heard the Joule and the Breeze), but I would not say they have a "warm mellow sound", which the OP is looking for. I also love my SP Tech speakers (just grabbed a pair of Revelations and have had a pair of Minis for a couple years), but I wouldn't recommend the SP Tech Minis to someone looking for "warm mellow sound". Let's not forget that audiophiles have different listening priorities, and try not to just recommend our favorites reflexively without taking the OP's stated preferences into account.

Some of Fritz's speakers would fit this "warm mellow sound" description, and Harbeth (along with other BBC speaker manufacturers) has long been known for that sort of sound. I'm partial to Fritz personally, but that would come down to personal preference most likely (Fritz's monitors would likely have considerably more bass, which is a biggie for me).

Ive had ref 3a decapo and lsitend extensively to kef ls 50.

for me, there no question, for weight, presence, tone, bass, imaging, the ref 3a is much better and can be had for 1.3k used