The G19 is a compact, so the 40 cal equivalent is the G23. The only 45 option in a compact is the G38, which uses the 45 gap round. If you're looking for old-school 45 auto, the only glock option to compare with your G19 is a sub-compact. The G30 (double-stack mag) or G36 (single stack mag). Both of those are awesome, but I personally prefer the G30 for the higher capacity mag (10+1).
Personal recommendation: Keep your G19, and go for a G30sf.