Hi there and welcome to BW forums.
First off I'm happy to hear you have turned away from CC.
Second, it sounds like you are doing the right things to regain trust and reconnect with your LO.
The thing to remember from here on is that with increased trust your LO will be able to slowly gain the skills and confidence to sleep alone BUT that confidence comes from knowing that Mummy (or Daddy) will always always return whenever he calls for you.
I think just continue what you are doing. Laying in the crib to help support and sooth him is a great idea (and no need for the pillow as this is a method to get LO off your lap and onto a firmer surface). if you can add a little rocking motion as you lay with him (as your LO is used to rocking) then you might be able to get him to finally nod off in there. I wouldn't even aim for him to sleep alone yet but rather to learn that it is okay to sleep in the crib with support from you...and later on to move yourself outside the crib but stay right next to him with as much hands on as needed to sooth and reassure.
I would avoid any sort of timed PUPD to be honest. it can involve lots of crying and could remind him of his prior experience of CC. In any case PUPD is a last resort method when other methods have been exhausted. So instead I would suggest always having a full wind down and soothing in arms then when in the crib put hands on firmly/reassuringly and give him that little rocking motion in the crib, use shush if he likes it or introduce a key phrase (you can introduce this right away and he will eventually associate it with soothing and sleep) which you can repeat like a mantra. Much later when you are working on him nodding off with your hands off him you can continue the key phrase to reassure (and hands back on/off to help when needed). Key phrase can also be used from outside the room once it is fully established to reassure your LO that you are there and still ensuring his safety even though you are not actually in his room - in ALL cases if your LO cries for you or calls for you then you respond with whatever level of support and reassurance is needed, ie if verbal reassurance from outside the room is not enough then you go in, if being in the room is not enough then you put hands on (and key phrase), if hands on is not enough you pick up.
After his experiences of being left I would take things slowly now. Keep reminding yourself that his confidence comes from you proving and demonstrating that you will always return, no matter what.
As I am suggesting more of a gentle withdrawal rather than PUPD you do not need to know "when" he is ready to start. Each step towards sleep training is small and with every step you take you can always go right back to full on cuddles. Even a fully independent sleeper has times when they need full on support, it doesn't ruin their ability to sleep alone or self sooth instead it re-confirms their trust in you that you will always return. As example, my DS was so independent with sleep that he didn't even want me in the room after his goodnight kiss but at times of illness or teething or tricky developmental leaps he needed lots more attention and at times I would need to stay until he was fully asleep, stroking his head but once the phase was passed he would return to falling to sleep alone again.
I hope this helps.