The most natural way to get your newborn to sleep is to feed and rock them to sleep. We all do it and that's what our newborn babies need from us. You can swaddle your newborn and pop them down in their cot on their back. Make sure their cot is clear from toys and bumpers.
I always recommend dummies for babies, if you are breastfeeding you may want to establish the feeding first.
The best way to do this is to have a thermometer in your babies room, work out the temperature at the start of the night, middle of the night and morning time.
Your newborn baby doesn't need an actual routine to go to bed but you cant start by giving them a bath, putting them in their night clothes, sing them a song and give them a feed and cuddle.
No, babies are not designed to sleep 12 hours. They wake frequently through the night for feeds, comfort, loneliness, cold and to survive.
You can safely co sleep if you are breastfeeding your baby, you must make sure you haven't been drinking, taking medication, smoke. Make sure your baby is on their back, become trapped, fall out of bed or get tangled in covers.