What about the security question recovery method? Is that method of recovery available yet?
If not then you should have to contact the support and I don't think it is really possible to recover if you lost the number so just get the same number by providing your ID then recover your gmail.
The only thing I can remember is the date the email was created and the device it was used to create the email, I either forgot it or lost it forever.
AFAIK the security question will be the one you set and answered while creating the gmail apart from that not much things were helpful in the recovery mode.So it is better to contact the support team and ask for any alternative methods.