I want to use this bag to haul my ski stuff to and from the mountain everyday, Which size should I get if I want to fit my ski boots, my jacket, a couple of layers, some gloves, and a helmet? The helmet can be attatched to a attached outside if need be. Thanks!

Tech Specs:

Material:

Phthalate-Free TPE Fabric 

Dimensions:

(small) 51 x 31 x 31 cm, (medium) 61 x 38 x 38 cm, (large) 71 x 41 x 41 cm, (extra large) 81 x 48 x 48 cm 

Volume:

(small) [2560 cu in ], (medium) [4200 cu in ], (large) [5600 cu in ] x, (extra large) [9070 cu in ] 

Backpack Straps:

yes 

Pockets:

2 interior mesh 

Weight:

(small) 1250 g, (medium) 1600 g, (large) 1820 g, (extra large) 2240 g 

Recommended Use:

traveling, expedition, moving, gear transpor 

Manufacturer Warranty:

lifetime