How old is your DS? We started using wool at about 3 months, and our DD used to wear a vest on her top half, but with poppers undone, with a nappy and shorties on her bottom half. She used to start the night in a grobag, and end up co-sleeping, so that was plenty warm enough
The vest as opposed to t-shirt made sure she didn't get an exposed midriff (as my gran would have said)!
If you feel the need you could get some extra big sleepsuits or vests and do them up over a wool soaker (you want to avoid constant cotton-on-wool compression, otherwise the moisture could 'press' though and make the cotton damp, hence the extra large sizes. You could also go for something like this which would be more slimline under clothing, but as I say we were fine with vests & shorties/soaker.
Other than that, here's my brief guide:
Buy some wool (shorties or soaker best for night, I think) - make sure you measure your baby OVER the nappy to get rise (top-centre-back of nappy right around between legs to top-centre-front of nappy), waist and hip measurements. Wool is better loose than tight.
Take delivery of wool, and with luck your seller will have washed (certainly!
) and lanolised the item before sending.
Dress baby for bed in WELL-BOOSTED NAPPY - You may have to experiment to find out what you can get away with at night-time; it'll depend on how much your baby wees 
See how you go 
If you need to wash/lanolise your wool it's not hard, you just need a bucket, wool wash and a pot of lanolin / spray. Not expensive. Follow instructions on product and refer to CNT / the cloth nappy contingent on MN if you need help.
Enjoy 