Help going from two Apple IDs to one I have two Apple IDs. One is with a gmail.com address and the other is with an icloud.com address. I have been using all of Apple's online/cloud/store services since they were released and have no idea how I ended up with two over time, but there is a clear distinction:

The icloud.com one has my iCloud - I sync iMessages in iCloud, have an iCloud drive, sync contacts, and use find my devices all on this account. I do not use iCloud backups or any sort of cloud photo features. I do not actually use my iCloud/.Mac email address.

The gmail.com one is logged into all the stores (music back in the day when I bought tracks individually, app stores, iBooks, etc).

I have a Mac, iPhone, iPad, and watch. I want to once and for all just have one login for everything Apple.

My thought is that since applications and other purchases cannot be transferred, I just need to transfer all my iCloud-synced information to the gmail.com Apple ID, then I can close or stop using the icloud.com Apple ID. I don't think I can go the other way since app purchases cannot be moved between accounts. Is this correct?

How do I go about doing this? Is it as simple as signing out of my iCloud account on one device, signing in on another, and repeating on each device, or will that potentially result in data loss or problems? What annoyances will I have to work around?

Thanks for your help.
As no-one has picked up on this yet, I'm gonna say "It's a toughie!" 

I had my first .mac account in the 90's, a private email address for iTunes since 2001 [which I consider my primary account, as it's still my 'real' email address] &amp; me.com [now also icloud.com] since the iPhone &amp; the App Store started.
I have never found any way to successfully merge these identities.
me.com has all my 'cloud sync' stuff, iTunes has all my apps. I have them both set to the same password so I don't have to think too hard about it… &amp; let it go at that.