How can I get warm water from my garden hose?
You might want to consider installing a utility/laundry faucet, in place of the spigot.  This will allow you to connect both hot and cold supply lines, and will have a built in mixing valve to allow you to vary the temperature of the water. They also tend to have the proper threads on the spout, to allow the attachment of a garden hose.



You'll have to find a way to support the faucet, as you don't want it just hanging by the supply lines. I've seen them with all different types of attachment methods, including holes to allow them to be screwed to the wall/washtub.  You'll also want to make sure you have a shutoff valve on each supply within the conditioned space of the house. It's also a good idea to have a way to drain the lines once they're shut off, if you live in an area with harsh winters.

The only other problem, is that garden hoses are not designed to be used with warm/hot water. So you may experience problems from additional contaminants in the water, to accelerated deterioration of the hose.