Training baby to sleep in bassinet

My baby is almost 3 weeks old and he hasn’t really slept in the bassinet for more than a short period of time. We have tried it various times but he gets uncomfortable and fussy. The flat uncomty surface I guess. My husband and I have mostly taken shifts with him staying awake to change/feed/ supervise him while he sleeps on the Boppy lounger downstairs while the other person sleeps uninterrupted.

Now that my husband has a week of vacation days we want to get serious about a bedtime routine that involves the bassinet. I have a feeling it’ll have to be a gradual thing to get him used to it a little bit at a time. We have tried swaddling and he doesn’t like it anymore and breaks out. I’m going to try a sleep sack next time. I have also heard about sleeping on the sheets of the bassinet so that it smells like you as a comfort to the baby, or putting a heating pad on the mattress before baby goes in to get it warm.

Does anyone have tips/ plan that worked for you on how to gradually get baby to sleep in his bassinet at night ?