My little one is about the same age as your DS. I (in theory) agree with the no cry policy and so far I have managed to pretty much achieve this. Some of the things I have taken on board however are these.
I let him catnap only if he's had a "biggish" sleep during the day.
I distract him if he wants fed more often than three hourly.
If he has a sleep I reward him with LOADS of cuddles and I always greet him when he wakes with smiles and cuddles and lots of positive words. I do this even if he's only had a 40 min sleep.
I am no expert but I think food and sleep are related. I think if they sip and snack on food they do the same with sleep and sort of get out of sync with what we need to survive as parents.
I would have a go perhaps for just 24 hours (or just in the day) to try and stretch the times between feeds if you possibly can. I would also try and stretch him between sleeps. Try and get him to "skip" one snack and one sleep so he eats a bit more then possibly sleeps a bit more.
I'm not saying stick to a routine but more try and distract him enough that he re-sets his eat sleep pattern.
Perhaps have a really "wild" exciting play time when he's threatening to nod off into a catnap. Then try and settle him with quiet play for a sleep perhaps 1/2 hour later......
Some stuff that's helped me is knowing babies sleep in approximately 40-45 minute cycles so they need to be able to roll from one of these to the next without our constant help in order to sleep for more than a catnap. I also know my little one sleeps better if he's had some hind milk.....he needs to have a decent feed.....and has had an active play (tummy time, swimming, being "danced about" by me) . I find my bloke has less good sleep days when he's been in the pram and less active.
The other good thing I found out was the "eat sleep play" pattern which meant I was using active then calming play before he tried to sleep.
I am sorry if this is alla bit disjointed but perhaps you'll find something useful.
Good luck to you, I personally would be terrified if I had to go to one of those sleep school places..........