Hi,
Ok, so there's a couple of ways.
The first one and the easiest way is to go to the iTunes Preferences, choose the "Devices" tab, there you can see the "Device Backups" section where it lists the backups. In that section it shows you the list of backups you have done in the past by telling you the name of the device and date it was done in. If you leave your pointer over the name of the backup it will give you more information of the device which that backup was done from, like IMEI, Serial Number, iOS version, etc...
That's the safest and most advisable way to go.
If you think there are still backups that this place isn't showing you, the 2nd way is you can always go to your Mac's system library and look into this directory: ~/Library/Application Support/MobileSync/Backup/ . There it definitely shows every backup this Mac has done via iTunes.
You can learn more about this on Apple's support article:
https://support.apple.com/en-us/HT204215
And by the way I wouldn't advise you to stop using the iTunes backup completely, because if in any case you have problems with your iCloud account, at least you will always a physical backup.
I hope this helps