My son just turned 15. He is 5 ft 10.5 inches and only weighs 110lbs (Ethiopian genes) with a size 11 boot. He has been snowboarding for three seasons and last winter was on his high school boardercross team. He has grown four inches since last winter but has gained only two pounds since then so we are confused on board size (we have gotten different opinions from sales people compared to the online sizing calculator). His previous board wasn't meant for boardercross either. Can someone please recommend what size and what board for boardercross (willing to go up to $1,000)? Thanks!