Birth Certificate and benefit proof is fine
"You can use a UK birth, adoption or naturalisation certificate, but you must send it with one of the following:
National Insurance card or a letter from the Department for Work and Pensions (DWP) showing your National Insurance number
photocopy of the front page of a benefits book or an original benefits claim letter
P45, P60 or pay slip
marriage certificate or divorce papers (decree nisi or absolute)
a gender recognition certificate
college or university union card, education certificate or PASS proof of age card (issued after June 2014"