From what you say and my experience with my 6.5m, previously a terrible sleeper, I would suggest that you try to take some time to give him a more consistent routine. Whilst I absolutely understand that when they aren't sleeping you would do whatever it takes to get them to sleep, I don't think it necessarily helps in the long run as their body clocks aren't attuned to a nap schedule, so you and they aren't ever sure if they are tired, and also they don't associate any one environment with sleeping, as they'll occasionally nap in the sling, the cot, the pram, car seat...
I'd think about where you would like him to sleep in the long run (probably the cot) and spend a week sticking rigidly to trying for every sleep in the same place and with the same environment (I strongly suggest dark, white noise if necessary, comforter/dummy if wanted)
Stick to an age appropriate routine: you can try:
Gina ford:
7am wake
9.30-10 nap
12:30 -2:30 nap (realistically he won't be doing 2 hours straight away, or possibly ever, but if not just make it up with the afternoon nap)
Around 4pm - nap to make up day time sleep to around 2.5h but no more than 45m, or no nap if 2h at lunch, awake by 5pm latest.
7pm bed
2/3/4:
7am wake
9am 2h after wake up, first nap, as long as he likes but no more than 1.5h
3 hours after waking from nap, second nap, take total sleep to 2.5h
7pm ish, bed
Do whatever you are comfortable with regarding settling, so if you are ready to do Cc then there are plenty of advice on this forum, if not, stay right by him in the dark and hold his hand/pat/shush... The important thing is to not take him out of the cot during the WHOLE nap time, or over stimulate him at all (so no pick ups at this age!). If he doesn't sleep, then he will at least be resting. I would then wake him up at the scheduled nap end time, do whatever you can to keep him awake until the next scheduled nap, and repeat. It shouldnt take more than 2/3 days for his body to get used to sleeping at these times, as the routines have the appropriate wakeful periods between sleeps. He should then settle more happily for naps. After a week of this, he should have caught up on his sleep deficit (as he's not sleeping well now), and you can think about doing a gradual retreat type of sleep training. It should be much easier as he will be used to his sleep environment.
I know routines aren't for everyone, but if a lack of routine isn't working, then why not try something different? I was convinced that I was not going with a routine for my LO, as I didn't want to be constrained by having to be at home for naps, and I wanted to be baby led. But for me, fact is my baby had no clue when he wanted to sleep (ie never!) and the routine has been the opposite of constraining - I know exactly when he will be sleeping and for how long so I can plan my naps, food, me time!
Happy to answer any questions!