Owning a car is a series of small, expensive surprises. Beyond the gas and insurance, the real cost is the wear and tear from everyday life. Winter is the hardest on the interior. Salt and slush ruin carpets fast, which kills your resale value later. You want to buy these before the first snow hits, usually late October.
Don't worry about financing the whole car on a card; that is for the bank loan. Use your Discover it® Cash Back to handle the specific upgrades like these mats so you don't feel the $200 hit all at once. It is a smarter way to manage your monthly cash flow while keeping the car clean.
Keep in mind that 0% intro APR for 15 months on purchases and balance transfers is a timeline, not a permanent discount. If you still have a balance after those fifteen months, the standard interest rate kicks in and the mats will end up costing you much more.