I have flown Virgin long haul at least 20 times, mostly with DCs in tow, and usually find them great - more child-friendly than most other airlines I have tried. You can get the odd surly/unhelpful cabin crew member whoever you fly with. Now I mainly choose Virgin for the entertainment system, but my DCs are 11 and 7, so that's the most crucial thing for keeping them busy on a long flight. Kids' meals and activity packs are OK, but I always take food anyway, as we are veggie and they don't do veggie kids' meals, and the food timing is always off - meals never arrive when they are hungry, it's usually just when they have fallen asleep.
At your DS's age, if he doesn't have his own seat, there's not much difference between airlines, tbh. I chose to fly Virgin when my DCs were babies because Virgin was the only airline to have special baby/toddler seats to strap into the main seat - but that's only relevant if you're buying them a seat anyway...
It's always sensible to take your own food, milk and nappies whoever you fly with - I think you can book an 'infant' meal with Virgin, but it may not be food he likes, and even if the airline normally carries baby supplies, you wouldn't want to rely on them in case yours was the one flight when they ran out. Make sure you check now with the airport about the latest regulations on what foods/liquids you can take through security, and again a day or two before you fly (it can change at very short notice).
Lots of chew toys is a good idea, though my two often spent happy hours playing with the plastic cups from the inflight meals and ripping up the inflight magazines and catalogues. Oh, and take plenty of spare clothes for DS and yourself.