Toddler keeps leaking through diaper at night - any advice?

Hello! I’m looking for help on how to help my almost 3 year old son stop leaking through at night. This has been going on for almost a month and we have had brief moments of respite (maybe a night or two), but then he is soaked again. We have reduced the amount of milk he has at night by half, we stop all liquids an hour or so before bed, we change his diaper for bed last minute so it’s as fresh as possible. We first switched from Pampers Nighttime Swaddlers awhile ago cause we thought maybe since they were swaddler style, that was causing the leakage (and maybe they were). We switched to Huggies Nighttime Pull-ups. We tried size 4t/5t since my son has a little bit of a belly (he is 39 lbs) and the 3t/4t looked really small. Well the 4/5 seemed to be too big since he seemed to be leaking through the legs. Then we switched the 3/4t and that seemed better, but then he was leaking through the legs again. Sometimes his waistband and bottom of shirt were wet too.

We thought maybe it’s just how he sleeps (he likes to sleep with his butt in the air and legs under him like on his knees, with his legs spread a little). We have tried changing his position, but he goes back to that. We changed from the Huggies brand to Pampers EasyUps size 4t/5t a few days ago. Two nights ago was a success, but he woke up this morning at 5 am completely soaked. His pants and shirt were all wet, his diaper was completely full and dragging down in the front.

He doesn’t have excessively wet diapers during the day (obviously that statement shows he’s not potty trained yet). We are at our wits end, poor guy. We have been in contact with his pediatrician and his endocrinologist about this issue. His endocrinologist tested his urine and everything looks fine there. I’m just wondering if anyone else has dealt with this and if there is anything else new we can try.

Thank you in advance!