I wouldn't buy a cert on that basis, yes you'll get a certificate for a Thomas Watson, no it may not be 'your' Thomas.
There are 24 births in FreeBMD for Thomas Watson born 1885-1887 in Lancashire.
So far the only clue is that he said in 1911 that he was born in Bamber Bridge. Hopefully that is correct and not just the first place he remembered living.
Until we know what he said his Dad's name and occupation was (from the marriage cert), we have no other checking point to use to attempt to find him.
BTW you didn't say if you have access to a site that lets you find him in the 1939 National Identity Register? If you can identify him in that it will give you his birth date, let us know as given you had 6 weeks to register a birth that could narrow down the options in the births index further.
Boo