how do you get your child to sleep in a bassinet??

Please help! My daughter is 3 weeks old and she won't sleep in her bassinet! I already made the mistake of having my 4 year old sleep with us when she was little up until last year🙈. Trying to change my ways this time lol but how do you make it more comfortable for them to sleep? The mattress is so hard but when I put her on my bed she falls asleep so easy or on this fluffy animal lay thing she falls right asleep.