If you don't have 2 pots that fit inside each other and the heating pad, do not buy them. You can instead invest money in yogurt maker, it cost less than the cost of a new stainless steel pot or heating pad.
185°F = 85°C
110°F = 43°C
In short yogurt making steps:
Sterilize all of the equipment
Heat milk to 185°F, quickly and evenly by using a hot water jacket
Cool it quickly and evenly to 110°F, using a cold water bath
Add or "pitch" probiotics from several capsules (4 - 10)
Cover and keep warm (110°F = 43°C) for seven hours, like overnight.
Tomorrow, you have one liter or more of fresh yogurt.
110°F = 43°C is the temperature at which the yogurt cultures (or your probiotics from the capsules, whatever strain you have ) will consume the lactose in the cow milk, and reproduce themselves. From each single bacteria you may get 5 000 or 50 000 live bacteria, converting lactose into yogurt acids.
You will "pitch" your milk with your strain of probiotics.