Sorry for confusing you (I do that a lot, but mainly cos I speak gibberish half the time!!).
Depending on DS's size you would need either a Size 2 or 3 nappy (DD has a HUGE bum and needed the size 3 by 19 months... in about size 5 pull ups if that is any help...).
I'll go back to the start...
Tots bots are made of terry, and the white ones are very very thick. You either get them that do up with aplix (velcro), or a nappy nippa (that's a little rubber doing up device, very very cheap and on ebay or one of the other sites I will list in a bit...). I prefer the nippa type - they are easier to adjust to the size of your child.
The tots alone aren't thick enough for a heavy wetter at night though, so you need either a proper booster - which is an extra 3 layers of terry specially designed to go inside the nappy for more absorbance. I had one booster, but then tried using a muslin square folded into about the same size as the booster, and it worked just as well (and is probably cheaper).
You then need a liner as well - if you are use to disposables, then it is probably easier for you to get disposable liners, which you can get in Tesco, boots etc. The liner stops the wetness going back onto baby's skin, and catches the poo.
Finally, comes the wrap - its what goes round the outside to keep all the wetness in. Again there are loads of different types - fleece, wool, PUL (sort of rubbery waterproof lining, soft outer). I use mother-ease airflow... it does up with poppers at the sides, which is good for little people who like undoing velcro!!!
Your baby will look like his legs are disturbingly far apart, but he will be fine (we all grew up with our legs disturbingly far apart, and still walk ok ).
The tots do take a very long time to dry, so a tubmle dryer is good, but if you haven't got one, then just getting a couple more nappies will do, so that while some are drying, you have more.
If you are doing nighttime only, then I would say 4 nappies, and 3-4 wraps (but I could be underestimating)... that way you wash every 3 days, with the 4th one on while they are drying, but that doesn't give you much leeway if there is one of the surprise poos just as you've got ready for bed!!! So maybe more... hopefully someone else can suggest!!!
websites... nappy lady - gives advice, and sells tots and wraps
The buzzness- sells tots... free postage!
Twinkle- sells tots and wraps
Tots Bots main site- sells tots and wraps
I don't know if that helped at all....