I co-slept with DD2 as she was very similar to your DS. I found that I would sleep on my side with my arm under DD's head. It is very difficult to roll in this position but easy for bubs to access the breast. Don't have any pillows or blankets around them and also make sure they sleep on the side away from your DH. From what I have heard/read, the mother will not roll on the baby instinctively but the father doesn't generally have that same instinct and can roll on them (however, seeing that your DH is moving to the spare room that won't matter as much). Make sure you don't drink alcohol/smoke/take drugs etc while co-sleeping.

If you take all the precautions it is very safe and genrally means better sleep for mum and baby (at least it did for us and pretty much everyone else I have known who has done it)