So you have been training since you were 17, right? I am very hesitant to tell someone what to use unless I know that they have researched this for themselves and know what's available and safe for women. Dieting and training are much more important than AAS. IMO the anabolics only enhances your chances of building muscle... without a clean high protein diet and intense training they are useless.
But to try and answer your question Ana Anavar (var) is by far the safest anabolic to start with because it rarely has any side effects. It's only slightly androgenic, however these side effects are possible: nausea and/or vomiting, nosebleeds, diarrhea, acne, deep voice, clitorial enlargement or increased growth of body hair.
It causes a dramatic strength increase (for me it does
) without the bloating (some women experience this though but I don't). Your muscles should become hard and defined. I gained some muscle on my Anavar (var) cycles but not anything dramatic. I really like it because it makes me so damn strong! I have chatted with many women that love it! And they have had dramatic changes in their body. We as women have to experiment w/ Anabolic Androgenic Steroids (AAS) to see which works best for us because we all respond differently. There is no way for me to tell you that you will not get any sides from Anavar (var) but it's less likely that you will get them from it compared to some other anabolic.
If you decide to use it after more research, start with 5mgs for 2 weeks to allow your body to adjust to the added hormones, then increase it to 10mgs and stay there for the remainder of the cycle. I am an advocate of longer low dose cycles so IMO run the cycle for a minimum of 12 weeks. I know it may be hard for you to stick to a clean diet for this long since it's your weak point but trust me your body will totally transform
Unfortunately, there's something else I need to add... this lifestyle is VERY addicting!
Saying you will do just 1 cycle is unrealistic! You WILL do another one so before you opt to start please think this over. You will love the way your body looks, the hardness of your muscles, the strength, the recovery. I am here to tell you that I am soooooo damn addicted. The recovery and strength is why I never want to come off. I feel so weak when I'm not on, that alone is all mental I know but I'm not ready or willing to stop.
Whatever you decide please let us know so that we can answer any questions you may have. Keep us posted on your progress! Good luck!