Ed,

I don't think this needs more of a melody than it already has.
The piano chording is really nice and contains enough "flavoring" notes to pass for a melody - or more "a dreamy improvisation".
The bass has plenty to say, too.

Don't think you need any "mixing advise" either. This is a very good mix.
Drums sit nicely. Bass has a great voice. and the piano sounds great!.

I'm listening for a 3rd time as I type this.
An excellent listen.
You could easily sell a whole album of this.
Would make great dinner/party/black-tie background music.

fj