I've been co sleeping with my baby since he was born. I think I've only done one full night without him in 11 weeks. The co sleeping 'position' is you laying on your side with your lower arm above the baby's head, and your knees curled up beneath their legs. In this position it is impossible for you to roll forwards on top of the baby, as your arm is in the way. Your DH can keep sharing the bed with you, it's up to you if you put the baby between you, or just keep her in your side by the edge. I use a blanket rolled up between DS and DH, and move it to along the edge of the bed when DS is on that side. I wake up as soon as DS stirs, without him having to cry, as he's close by and I'm aware of him at all times, even when asleep.
The risk factors are smoking, drinking, drugs/medication, deep sleepers, memory foam mattresses, saggy mattresses, duvets and pillows. If either you or your DH come under the first few, you shouldn't co sleep. If your mattress is memory foam, be aware this is warmer and dress baby a little cooler. Saggy mattress can be a risk if its likely you, DH or baby can roll into the middle onto baby. Duvets and pillows are ok on the bed, but should not be on or near the baby.
I bought a large fleece blanket for our bed so DS could share with us. Alternatively you should bring duvet up to your waist (not on baby at all) and cover baby with their own breathable blanket.
As for feeding laying down, the key I found us position of your shoulder on the bed. If you move your shoulder away from you toward baby, your nipple will angle up higher toward ceiling, move shoulder underneath you and your nipple will be lower. Once your at the right height, put your DD on her side beside you, lining nipple height with her nose. Figure out pillows to keep your head and neck comfy, and maybe one behind you that you can lean back on (or your DH).