With a block heater and garage nap time, I think you'll be fine even with the oil you've been using thus far.
I'd be more worried about the car rusting apart at the seams vs the engine wearing out from Lube related wear. Lol.
Definitely go with a synthetic 0w20 (like Mazda spec's for this engine) if you plan to run the maintenance timer down to 5% oil life remaining vs what you're doing now, which is probably 50-70% oil life remaining when you drain it out after 6-7km.