You'll probably find winter tyre sizes in the handbook or possibly on the tyre pressure sticker (fuel filler flap?), that would be a good starting point, then find the correct sized wheels to suit, probably 17 or 18" (doubt you'll get 16" on with the size of the brakes but you never know) off a lower properly specced model.

Alternatively your dealer service desk should know what size wheels and tyres you can fit instead.

If you go full MT tyres remember you'll be getting something like 13mm tread depth and a pattern not really suited to on road use, so squishy handling plus noise plus not so good warm wet road grip, you still find 13mm tread on some AT tyres, but these should be less aggressively patterned than MT's, so more suitable for all purpose.