So the saga in getting a business adsense account ready for the YouTube channel is not over. As expected I received the "you already have an adsense account associated to you" type email from my previous attempt so I created a new email and applied with that one instead - this time adding my business name (which quite clearly states to put your business name btw - something I completely missed previously). Fingers crossed.
This morning I got an email in response saying that I already had an account. This one was different in that it was saying I had an AdMob account with a partially obfuscated email that I didn't recognise at all. Somewhere in my brain I vaguely remember signing up for Admob. So I tried signing into Adsense with other emails I had used for my business. Lo and behold one of them was connected to Admob - I suspect they use a random email when adding to an Adsense to stop duplicate account issues or something? Who knows.
So I have attempted to add website Adsense to the Admob/Adsense account but perhaps I'll be able to add this account to YouTube anyway. We will see what happens but I'm hoping this is my ticket to getting a business account on the YouTube channel once the Monetisation eligibility is (hopefully) approved. Automation in this case has certainly overcomplicated things but I haven't helped the situation either.