Spaying sows is only necessary when they have real trouble with ovarian cysts, otherwise it's enough when the boar has been neutered, which is a far easier option.
Most boys are neutered, because they wouldn't get on with other boys at a rescue and are looking for a girl to share their life with.
However, you can pair sows of any age; so that is another option. I had two nearly three year old become the best of friends!