Thank-you for your advice Kelly.
Today I tried keeping him up the extra half hour in the morning, but it was all a bit of an odd one since he slept in until 7.15am (heard him wake with a quiet cry at 5am, but he went back to sleep himself) so I think that's thrown him off. He wasn't asleep until 3.5hrs A time at the start of the day. He also had a 2.5hr nap yesterday which is odd for him, so maybe he was catching up on sleep. Will try again tomorrow.
He doesn't fall asleep independently for naps, I hold him until asleep then put him in his cot, but I don't need to feed to sleep for naps. He did self settle until he was unswadddled at 6.5months, since then he's struggled with sleep. I tried for a while to shhh pat which is how I had him learn to self settle initially, but it just kept resulting in him screaming and seemed to make him more upset and angry. After weeks of this we were both stressed about nap times, so I decided to hold him until asleep because it was all too much. I knew I'd need to 'fix' this further down the track, but at the time it was what I felt I needed to do.
Like you said, one step at a time, which is why I hope to sort out an appropriate routine for him, and then tackle getting him to fall asleep in his cot.