Historically, liposuction surgical treatment to reduce limb volume is utilized in lymphedematous limbs when limb enlargement can be attributed to fat deposition as a consequence of  lymphedema. The actual liposuction technique  differs from that traditionally employed for removal of fat. The surgical procedure should be done only by surgeons trained in the specific technique and well versed in treatment of lymphedema.  Worldwide there is a select group of surgeons who meet these criteria.

Prior to surgery, by current standards, the lymphedematous limb's fluid  must be in excellent control. After the procedure, it is imperative for the individual to  continue lifelong, persistent, diligent decongestive therapy and manual lymphatic drainage alongside good skin care practices. Without continued lymphedema treatment and care, the enlargement returns. Liposuction is not a cure and all surgical procedures carry risk of complications.

You mention you have always had "big thighs"  relative to the rest of your body.

Without actually seeing what you mean by "big thighs", one thing that comes to mind is "lipedema." Lipedema is a chronic condition of proportionately larger, symmetrical deposition of fat on an individual's thighs and legs. Different authors describe not only alterations of fat metabolism and distribution but also alterations in lymphatic vessels and lymphatic function in lipedema.  Often inherited, it's characteristic features can often be seen in other female family members.

Since liposuction is not a cure and all surgical procedures carry risk of complications, I would encourage you to enlist the help of a trained lymphedema therapist in your pursuit of smaller thighs. Successful reduction of thigh size in individuals with "big thighs" and lymphedema can be achieved with non surgical interventions.