Saggy breasts after breastfeeding - Need advice!

I'm still breastfeeding my 2 years old son. I thought of stopping it when he was 1.5 years old but he doesn't eat anything else and he was underweight. So my GP advised me to gradually decrease the time of breastfeeding and then stopping it or else it will affect my baby's health.
My boobs were already saggy before pregnancy but it was not weird. But after delivery and breastfeeding (3 children) my boobs are horrible.
While researching online, I saw that certain exercises can help to make the boobs firmer and I started trying it. But after a few months, I understood that there are certain things no amount of exercise can fix, and the sagginess of my breasts was one of them. lol.
I was under depression so one of my friends suggested breast lift surgery from a clinic in Windsor. I'm afraid to go under the knife, but there is no option left for me. This sagginess is affecting my health. I'm suffering from shoulder and back pain. I would like to correct it before the situation gets even worse. Any advice is highly appreciated. Thanks!!