I would say give it another month before he starts firming up! DS is 11 weeks and I would say from about seven-eight weeks he started really building up strength. He has always had pretty good head control for his age (I think having him upright in a carrier a lot rather than laying down all the time helped) but he started finally lifting his head up properly in tummy time last week. I have also noticed in the past week he is becoming slightly more deliberate with his hands: putting them in his mouth, batting at toys, bringing them together and opening them up rather than just thrashing about with them.
Take a look at this: https://www.youtube.com/watch?v=WoB6ReAenR4 Although don't (like I did) look at it at, say, 7 weeks rather than 2 months and then worry that he isn't doing as well as the 2 month old, because they really change so fast in just the space of a couple of weeks!
Thanks for sharing your experiences the video is really interesting, I think my baby is am quite far away from the normal development at the moment but hopefully in a couple of weeks he'll be there.
We also use a carrier lots, we don't actually own a pram and he's not happy when put down so he's carried most of the day. He's pretty good at holding his head up when he's angry and throwing and throwing his head backwards in the sling!
He's a really big baby, he was nearly 11 pounds at birth and he's put on weight quickly so he looks like an older baby, just a very floppy, sleepy older baby.