Sleep training?? 😴 HELP

So my 4mo used to sleep wonderfully..naps and at night. I was leaning towards it being a regression but I brought it up to his peds and she said he should be fighting sleep all the time (he still sleeps through the night once I finally get him down). So he used to sleep in the bassinet pack n play next to our bed..then about 3-4 weeks ago he started fighting sleep so bad every time he was tired. He still fights occasionally but not near as often or for as long. Now here is the thing.... he has been sleeping in his rock n play or swing (no bashing, I already know he shouldn’t be sleeping in it) or occasionally in our bed which I do NOT want to make a habit. I have tried to let him sleep an hour or 2 in his rock n play and then transition him to his crib (I’ve also tried putting him back in the pack n play but he hates that now too) but he wakes after a few min and I usually fight with him for an hour or 2 with no luck..I used to move him to his bassinet all the time no problems. I assumed he doesn’t like laying flat BUT he will fall right asleep if he’s put in our bed. I know he wants to feel snug but he can’t sleep with blankets and is rolling over so can’t swaddle him anymore. He also doesn’t take his paci anymore. We also have a bedtime routine that we’ve been following for some time. I guess I’m just asking for advice..I feel defeated and I’m so lost on what to do. Someone please help 😫

ETA: I’m not opposed to crying it out, just don’t know how to approach it. How long do you let them cry/how often to go in/do you pick them up etc