RECOMMENDATIONS NEED: CallRail + ___ CRM ?

Currently using CallRail as our main communication platform with inbound/outbound clients (phone, SMS, forms).

Issue we're having right now is keeping track of follow-up calls, or leads that failed to convert into a sale. We are using a mix of CallRail tags (FOLLOW UP), CallRail notes, and Excel sheets to keep track, notify each other (3 call reps) of any follow-up calls made, etc.

So far, our trials of CRM integrations with CallRail have fallen flat.

Does anyone here have any recommendations?