Sunken Cheeks: Long-lasting Dermal Fillers Available?

You sound like a perfect Sculptra candidate.
Fillers do go away in months and if you need considerable "plumping" the cost of repeating temporary fillers can get very high.
Sculptra was originally approved in the US for treating lipo atrophy in patients with HIV over 5 years ago. Lipo atrophy (or fat wasting) is not a problem only for those with immune deficiency, but also for some with high metabolism, from weight loss, or just genetics predisposition.
Sculptra is injected in such a way to restore volume in nearly any area of the face. Done well, you can fill out the central face, cheek areas, temples and the fill effect from above can "lift" the jowls.
The volumizing effect comes from your own collagen since Sculptra's job is to activate new collagen production. Obviously your own collagen will be less prone to breakdown than a gel filler. Many patients enjoy prolonged volume improvements of 2 years or more....this is all dependent upon your own body's system and health, but you should certainly expect a good 18 months.
I was fortunate to begin working with Sculptra while it was being investigated years ago. My patients in the Los Angeles clinic were thrilled to "get their face back". The work and research opportunities I've had led to my becoming a trainer for Sculptra and I love seeing what it can do for such a wide variety of people.

Thank you for your question. For long-lasting facial volume, your options are facial fat grafting or a collagen stimulator like Sculptra. Facial fat transfer takes small amounts of fat from another area of the body and injects it into the face to create the volume you want. You mention you are not a candidate for fat transfer, so if this is really the case, Sculptra might be your best bet. This collagen stimulator is injected deep into the dermal tissue, where it triggers the body to produce more collagen. As collagen levels rise, the midface becomes fuller and more defined naturally. It can take a few months for the results of Sculptra to fully develop, but improvements can last two years or more. I recommend scheduling a consultation with an experienced, board-certified facial plastic surgeon who can assess you in person and create a customized treatment plan to meet your needs and goals best.

Hollow or sunken cheeks are difficult as the filler needs to be both high volume and smooth.  Sculptra will stimulate collagen over time and is excellent for this application