Adopting step children.

Ladies, I have a son from a previous relationship that ended as soon as I found out I was pregnant. long story short my sons father died, he took his own life when my son was 4 months old. My son never really saw him and I was a single mum until I met my now fiancé who has stepped up to the plate and become daddy. My son calls him daddy and all he has ever really known. this man has brought security, consistency, love by the bucket full, completes our family, goes above and beyond to support us and is my sons whole world, the two of them simply adore each other and it's as if they really are father and son. Am I wrong to have my fiancé adopt my son? I don't intend to ever hide the truth from him, he just has to be of an age that he can understand. I feel my fiancé deserves the parental rights, the recognition and everything that comes with being a parent! Because after all it's him here doing it all with me. I just want it cemented that we are a family unit and we will all have the same last name so my son won't feel like a "outsider" 
Also has anyone else done this in England? How did you find the experience? Do you regret it?