Congratulations!
I think from your list [name_m]Frederick[/name_m] would go the best if it wasn’t for the nickname [name_m]Freddie[/name_m]. I do think people would default to Fred/Freddie, which you could spend a lot of time correcting. I do like August/Augustine but would probably avoid as [name_m]Augustus[/name_m] has already been used.
Some suggestions (any repeats are another vote for the name!)
[name_m]Ernest[/name_m] ‘Ernie’
[name_m]Wilfred[/name_m] ‘Wilf’
[name_m]Albert[/name_m] ‘Albie’
[name_m]Reuben[/name_m] ‘Rue’
[name_m]Montgomery[/name_m] ‘Monty’
[name_m]Stanley[/name_m] ‘Stan’
[name_m]Reginald[/name_m] ‘Reggie’
[name_m]Barnaby[/name_m] ‘Barney’
[name_m]Douglas[/name_m] ‘Dougie’
[name_m]Ambrose[/name_m] ‘Bram’
I saw you had [name_m]Atticus[/name_m] already suggested as a first name and I wanted to add that I quite like that as a middle alongside [name_m]Augustus[/name_m] & [name_m]Aurelius[/name_m]. 