I understand why you want to breed from your mare. I also bred from my older, maiden Thoroughbred mare because I loved her so much and wanted a foal from her.
Like yours, she was in great health and 19 years old. I made sure to use a well-respected vet and used AI. I had never bred before, and had a lot of people telling me that everything would go wrong, but I refused to panic.
I rode her for the first few months before giving her the rest of the time off.
I did everything I was told by the vet, and she had a healthy colt over night. The only issues came after the birth when she had trouble accepting ber baby. But I worked through those too, and within a week she was in love with him.
My mare has since passed away, at age 26, and I miss her every day. If it hadn't been for her son, I would have given up riding. As it is, he and I are now successfully winning First Level dressage together. I love him to bits and we have a very strong bond.
I'm not saying the others are wrong to suggest buying a foal. I think it is cheaper in the long run. But the satisfaction of breeding and training your own horse is unbelievable and not to be left out of the equation.
Good luck with your decision.