I have several things I use. I started with the rolled up socks but too hard and not appealing. Tried rolled up stockings but not big enough. Moved on to bath scrubbies in a nylon stocking and it works to make round boobs. Then got idea I wanted pointy boobs, a nerd football cut in half then coveted in nylon stocking nude color. That worked great and I luv the big pointy tits. Of course bigger is better, bought two more footballs and cut them at about 2/3 size, oh yeah nice, big, pointy, fun, sexy.
I use silicone breast forms. You can order them off EBay and they are fantastic. They look and even feel real and you can order a set for around $35 to $100 depending on how big you want to be. Mine was about $60 but I have had them for a few years. Mine make me a 44D
I have tried several things to give me boobs that look realistic. Large, soft nerf balls work very well in a large bra. The balls are very comfortable and give me a size 38″ chest. I have also tried water balloons but found they are too cumbersome and take too much time to fill each time and drain afterwards. I also tried a cheap set of plastic tits I bought at a halloween supply store, but found them to be uncomfortable and not easy to use a bra with them.
I have a pair of silicone breast implants I use. I cannot say where I got them. They feel great. See my latest pics for what they look like in my wifes C cup bra. The D size implants peek out, but still look good.