You need more charcoal. I think your basket is too small.
My firebasket is 16" diameter and 12" tall. I fill it about 3/4 to full every time I cook no matter how long I am cooking for. I normally light about 15 coals and put on top of the unlit coals and let the UDS sit for about 45 min before it is up to temp and the thick white smoke subsides. With my basket I have cooked 16 hours and still had coals to snuff out when done. I do this just by closing all the intakes and exhausts. I just add to the leftover coals for the next cook as needed.
Do a quick search for "Minion Method" and you will see tons of ideas.