I got the X3 winter package from simply tire in toronto. Highly recommended.
I picked the 17" with Toyo Observe Gsi-5. They offered a bunch of other common ones by Bridgestone/Continential/Dunlop/Michelin but I decided to go with Toyo based on some personal recommendations. Came out to $1400ish taxes in after all the discounts/rebates. Was pretty pleased.
AND, in contrast to what BMW said about requiring 18" on the 35i, the 17" I got fits perfectly, and no TPM needed.