I'd still swaddle, maybe just a bit looser. Especially if he sleeps on his back. The startle reflex that wakes up back-sleepers continues until about 6 months.
If he's not sleeping as long, either swaddled or not, you could try propping him on his side with rolled blankets. He's probably a natural tummy sleeper and once he's able to roll over onto his tummy, he'll sleep great.
(Personally, I'd put him to sleep on his tummy now, but I know people have the irrational fear of SIDS beaten into them by the BTS campaign.)