Preface: I will refer to no ADS, no point fire as neutral stance.
CQC-Control-Scheme (FPP):
L2 (toggle): point fire
L2 (hold): full ADS
Make it that when you are in point-fire mode and then hold L2 to go into full ADS and then let go of L2, it returns to point-fire mode. When you go full ADS by holding L2 from neutral stance and then let go of L2, have it return to neutral stance.
When in point-fire mode, make it that the player cancels out of that mode when pressing L3 to sprint and can sprint away immediately. That way players are not trapped in that point-fire mode when they want to do an evasive maneuver.
L3, R3 (toggle) whilst in ADS: lean left and right
Make it that when you are leaning right and then press L3, the character makes the full motion to leaning left. Same from leaning left towards leaning right via R3. This allows players to peak slim objects such as trees and pillars effectively from both sides.
Remove ability to lean in point-fire mode to enable cancellation of point-fire mode via sprinting mentioned above.
L1 (toggle): hold breaths whilst in ADS
This would still be a bit awkward but you would mainly use this for sniper shots from a strong position. So here having to use middle finger to hold L2 and press L1 to toggle hold breath would be ok.
CQC-Control-Scheme (TPP):
L2 (hold): point fire
R1 (toggle) whilst holding L2: full ADS
Toggling allows the player to return to point-fire-mode.
Letting go of L2 whilst in point-fire-mode or full ADS let's the player return to neutral stance.
L3, R3 (toggle) whilst in point-fire-mode or full ADS: lean left and right
Love your game, hope for many years to come!