Which procedure, excluding tummy tuck, would help tighten loose skin on the belly?

As you stated, there is surgical excision which is the gold standard for skin laxity tummy tuck and you would have amazing results because you area laready very lean, and some muscle repair would return your waist line and you would be long, lean and narrow waisted but...
The best treatment for skin laxity that is not surgical is Renuvion for a couple reasons. It has the most effective and durable results and it is a singular treatment. There are many treatments such as Morpheus, US, cryo, etc that are all intended at creating some form of inflammation that can lead to new collagen formation. Renuvion is the most effective at neocollagenesis because of the amount of energy that you can deliver by doing it fron underneath the skin. Renuvion also tightens the fibroseptal network which none of the topical treatments can. In this way, there are two waves of results, the first is the tightening due to the fibroseptal network and then the second wave is due to the new collagen which shrink wraps everything.
Important to know that the full effect of Renuvion takes 1 year.
In someone like you, this would be done in the office with oral sedation which would decrease cost significantly.
We would be happy to discuss how we make it easy for patients to fly in and have a mini-vacation with us in Tampa if you would like to come and visit. You would only need to stay in town for a day or two, and wear a garment for 2-3 weeks. You could start working out again in 2 weeks. Other than the garment, it would not be apparent to those around you.

Hello; We use for tightening that, there are devices; such as Renuvion J Plasma, Bodytite or injectional applications; such as PLA (Sculptura, Lanluma). However, after the implementations, the content of tightening; it always depends on the skin quality. If there are many or wide cracks on the skin; the volume of tightening will be less.