Heavy wool drapes on that window may help. Wool army blankets are useful for experimenting.
Are you sure you can't do long wall placement? Your listening position would be close to the back wall with this placement, so you'd need to treat the wall behind your head (4" thick panels should do it. ATS Acoustics makes some inexpensive 4" panels).
Are you sure you can't do long wall placement? Your listening position would be close to the back wall with this placement, so you'd need to treat the wall behind your head (4" thick panels should do it. ATS Acoustics makes some inexpensive 4" panels).