I have a problem with knee & hip pain and thought the SG was a little cramped also. I put some highway peg on, that I really like. I leave the ball of my foot on the hwypeg and rest my heal on the front part of the floorboard. I use my right heal to brake and move my left foot on to the board only when I up shift. I down shift with my left heal. This arrangement might take a few miles to get used to but it made the difference of riding my SG or looking for something else. On the handle bars you have several options, the stock ones worked for me. Lastly you can spring for a seat that moves you father back and possible up a bit higher. I am a big Corbin seat fan. This in the first bike in the last 6, I have not purchased a Corbin seat. Every other bike I have had, caused, major tailbone pain. Each time I replaced the seat with one from Corbin and the pain went away. Corbins seats are on the very firm side. If you like plush it is not for you.
The pegs are by far the cheapest and most beneficial change you can make. I had a friend who was always complaining about knee pain and I tried to talking him in to my method several years ago but he is quite stubborn and did not want to try shifting and braking using a different method. About a year more of pain and frustration he was ready to look at a Yamaha that had a bit more legroom. I said it would be cheaper to give my method a try first, and this time he listened. It took him about 2 weeks but he called me up and said that he owed me a good bottle of scotch because he was not having the hip and knee pain anymore, and it saved him a ton of money.