What procedure is best for loose skin on the stomach, inner thighs, and upper arms?

While it is difficult to make a recommendation without seeing the extent of your skin laxity, it is very likely a nonsurgical skin tightening treatment could be a good choice for you. I offer ThermiTight, which is a device that delivers radiofrequency energy into the underlying dermal structure via small probes. The RF energy heats the tissue to constrict it and tighten skin from the inside out. At the same time, the treatment boosts collagen production to provide support to the dermal structure while firming and smoothing the outer dermis. 
ThermiTight is a nonsurgical procedure with minimal downtime afterward. It can be safely used on nearly any area of the body and results can be long lasting. I recommend working with a board-certified dermatologist who has the expertise and qualifications to ensure your procedure is both safe and successful. 

Bodytite is very effective at tightening tissue and making the skin envelope appear tighter, but there are limitations to any of these less invasive procedures with regard to skin improvement.  BodyTite is a non-excisional device that utilizes radio-frequency assisted lipolysis (RFAL) to address the shortcomings often associated with traditional liposuction or surgical body and face lifts, including sagging or wrinkly skin and scarring, by inserting a wand under the skin to coagulate inside while tightening the skin on top.  BodyTite can be combined with liposuction to improve contours dramatically. Results can be seen immediately after one treatment and are more evident over three to six months post-treatment. Wait until six months to full evaluate the aesthetic results.  Sedentary activities can be resumed in two to three days and full activity with exercise within two to three weeks. 

Thank you for your question. At my office, we have seen great success with BodyTite and Morpheus8 when they are used together to tighten skin around the body. BodyTite uses a bipolar to transmit radio-frequency energy to your tissues. It is inserted through small incisions that give your surgeon access points to the areas of skin laxity that you want to treat. Morpheus8 is a microneedling treatment that uses radio-frequency energy as well. It works on resurfacing your skin, remodeling fat, and stimulating collagen and elastin production. Be sure to visit a Board Certified Plastic Surgeon to ask about your options.