Hi English Daisy
You may have already found him already but I have managed to find John Thomas in 1851! This time living at Upper Water Street:
John Thomas (44) Head, Married, Master Printer Employing 3 Men, Born Carmarthen
John Morgan Thomas (19) Son, Printer, Born Carmarthen
Both of these tie up with the 1841 Census entry
Plus living with them were:
Mary Thomas (39) Wife, Born Neath
David Godfrey Thomas (4), Born Llanelly
Henry Griffith Thomas (1mth), Born Llanelly
Mary Eliza Thomas (2) Born Llanelly
Given the 3 younger children were born Llanelly (and all less than 10) that John Morgan Thomas was born in Carmarthen and in 1841 there is no mention of Mary I wonder if Mary was his second wife?
Anyway, hopefully there is enough there to keep you busy!
Roy