My house is 70 years old and the main shutoff valve for the water is leaky, so I'd like to add a new valve. It's regular 1/2" copper, which I'm usually comfortable working with, but the problem is that since the valve is leaky, I don't know if I can keep the pipe dry long enough to solder in a new valve downstream of it. I don't know if I want to use a sharkbite fitting for such an important location, since they seem to be unreliable in the long run. Copper compression fittings seem like the ideal solution here, but require an expensive power tool I don't have and which the hardware stores don't seem to rent out.

Am I missing an option here? Do I need to pay someone to come in and crimp a valve into place?