I don't know how old you are but keep in mind, much of that appearance is a result of your body structure, i.e. your bones. Testosterone during puberty drives bone growth that results in a broader shoulders, larger hands and feet, etc. Once bone has grown, you cannot reverse that. So what I'm saying is, the super petite look that you're striving for simply may not be achievable.
To maximize your results however, there are a few things you can do. Managing your diet is paramount among them. Losing weight will cause not only fat loss but some muscle loss as well. Additionally, if you're not on Hormones at this point, the muscle loss that is an effect of Estrogen could also help you achieve a more petite appearance. However, while losing muscle mass will help, you also need to be realistic. What you should be striving for is for a body whose proportions are feminine. Women come in all shapes and sizes but for us trans women for whom testosterone has already done it's damage, some of those sizes just might not be attainable anymore.
For instance, I too am very broad shouldered. I wear a size 6 jeans but have to buy size 8 or 10 dresses to fit over my shoulders and chest. With HRT and some diet, I should be able to get down to a true size 6 dress, but the reality is I'll never be a size 0 or 2. I've accepted that and I'm ok with that. At 5'10", a size 6 is a very attractive woman and I think for all of us we'd be ecstatic just to be an attractive person of the proper gender.
One other thing you might find helpful (I have) is the What Real Women Look Like website. You can filter images of real women by height, weight, age, pants size, shirt size, and body type. Put in values that closely match your own and you can get some idea of what might be possible.
http://www.mybodygallery.com
