ayyy I got you. So check out 7th and 9th chords like folks have been saying, but for a modern jazz sound, also check out/mix in quartal chords as well. Here's an example:
instead of playing Cmaj7 with a 9th, which is
c e g b d
play a quartal version
c e a d
e, a, and d are all a fourth a part. d, the ninth, is still the top most note, so you keep some of the properties of the the maj7 version, but the fourths lend it this super striking quality. It can help to kick that c down an octave.
ALSO check out quintal chords. Like, instead of standard fm7
f ab c eb
we're gonna get all wiggy.
f c g ab eb Bb
f, c, and g are all a fifth apart. same thing with ab, eb, and Bb. The result are these huge, rich chords.
Other stuff you should check out: secondary dominants, ii-Vs, and different voicings. Here are some helpful videos.
https://www.youtube.com/watch?v=I-bZje31xsYhttps://www.youtube.com/watch?v=AJYRX5YW_eIhttps://www.youtube.com/watch?v=YeXueyqh4JE