My little man is exactly a month older than yours and he has also be determined not to settle himself to sleep.
I've finally started controlled crying/comforting (started tonight) as I have tried all sorts of other things including sitting with him (for an hour or more!!), feeding to sleep (he'd wake as I'd detach him from my boob), bringing him into our bed (then he feeds all night!!), music, toys, etc. After 40 minutes this evening he finally settled himself. I went in and out several times which would calm him, then upset him as I left, but he eventually fell asleep on his own. Fingers crossed it works during the night!!
The other thing I've noticed with James is that he is generally more clingy at the moment. I've heard that separation anxiety is often at its worst at 12mths which may be the problem and maybe thats why your little fella is suddenly not settling.
Sorry I can't really help you though. Hope you find something that helps.
Best wishes, Diana