Hold on for the ride. My Stumpy is now almost 20lbs and 14" long and 10" wide at 1yr. 8.5months. Will probably be 25lbs at 2 years. Just posted a photo of him by the wood stove and those bricks are 6.5 inches. I have another little one that is growing slower... thankfully.
So the heated house is the best option. Sometimes tortoises refuse to stay there and you'll need to train them.