You might find it handy to use a tailor's ham when pressing. If you're wondering what a tailor's ham is, this is a great definition from Wikipedia:
A tailor's ham or dressmaker's ham is a tightly stuffed pillow used as a curved mold when pressing curved areas of clothing, such as darts, sleeves, cuffs, collars, or waistlines. Pressing on a curved form allows a garment better to fit body contours. To accommodate tapering or garments of different sizes, it has roughly the shape of a ham.
A tailor's ham will run you $9 - $20 to purchase one new. Although that's not a ton of money, there's no reason you can't make your own from scraps of fabric you have laying around. I created a full-length video showing the entire process. There is also an edited version, if you don't need all the details to make your own.