I am the queen of dealing with big babies (both my ds have reached 17lb by 3 months)
Ds # 2 who is 17lb & not quite 3 months (10lb 4oz born) is still swaddled. I use a cot sheet or 1 mitre x 1 mitre muslin square.
I fold one corner down & place his neck where the fold is, tuck his hands under the folded bit ( he sucks his fands) up near his face. then I take one corner & wrap it over, then wrap the other side over, then fold the bottom un & then tuck under... i used to wrap a second one around him, but didn't include the hand wrapping, but I'm gradually weaning him off the wrapping. This is a variation of the Aussie Swaddle ( see announcement at the top of this forum)