If he is self settling with little or no fuss at 6 weeks that is fantastic. I have been told that babies that can self settle and are younger than 13weeks generally cat nap for two reasons - hunger and coldness. You may need to increase your feeding, every three hours and if you are breast feeding make sure you have lots of protein in your diet. My nurse who is 70 and been doing this for a long time says BF women need 5-6 serves of proteina day, starting as soon as you wake in the morning ( meat, yogurt, milk,tuna, cheese. (bubs do have a growth peak at 6 weeks too)
Try to put one more layer on him too .
Also you maybe going in to soon, lots of babies makes some noise in between sleep cycles.
If you keep your sleep rituals the same it will get better.
Both my bubs catnapped one from 6weeks and the other from 3. and now they are both good sleepers.
(PS my nurse also says the dummy is ok till about 16weeks so i say use it if it helps.
GOOD LUCK i know how upsetting catnapping can be