1st and probably the most obvious and cheapest issue:
Try cleaning the boost control valve on the front strike plate... Open the circular end cap with a small flat blade screwdriver. Remove the foam filter and give it a wash. Allow it to dry and use carb cleaner and a tooth brush to get rid of the grime inside the valve body where the filter sits. Remove the pipes and label them, spray carb cleaner down them.
Refit it all together and then try the car.
2. Egr as already mentioned. Blank it for a few quid to see if it eliminates the hesitation.
3. Try another members fuel rail tuning box at a local Alfa meeting. I'm sure someone would let you try it, I would!
It takes 5 mins to fit then take it for a drive, if the issue disappears, then you have a lazy high pressure pump hesitating on light throttle... Save a fortune on a replacement as there is obviously nothing wrong with it on the higher demands of delivery. Get your own tuning box and appreciate the extra benefits of better power and torque instead.
4.. be happy you've saved a fortune!