Success.
I, too, have been through this dark tunnel and after a week my account has been restored.
First, you need to promote one of your Gmail accounts with the domain ending (not a gmail.com ending) to super admin using this form: https://toolbox.googleapps.com/apps/recovery/form
This form works even if the account is suspended. You will need the username and password to your domain hosting site to do this (the GoDaddy/OVH/HostGator kind of companies that you pay annually to host your domain). Follow the instructions on the link to add a CNAME or TXT to your domain - I didn't have a clue what that meant, but just followed along blindly and got there in the end. After this, the Google recovery form will be stuck for a while during the verification step, I clicked the 'check again' button every half an hour or so until, after about three hours, it took me to the next stage. You have two choices: I chose the first option (Request User Promotion). It says this process will take 72 hours - in my case, it took five days.
You will not know when your account has been promoted so you need to check regularly. I used this form: https://support.google.com/a/answer/2855120 and clicked on 'I used my account for personal use'. For four days, I was faced with a 'you need an administrator account' blocking screen. On the fifth day, my click took me to a previously unseen workspace page, where I needed to answer a few questions (I hit 'set up later' when it asked about billing), then, after the questions, looked again for the option 'this account is for personal use' and clicked. Bingo.
I am really not an expert in such things so forgive me if my technical jargon is inaccurate, but that is how I recovered my suspended Gmail legacy account.
Steve
LinkedIn
Twitter
