Medical science does not have a magic pill YET to prevent facial fat loss whether it occurs as part of aging or as part of overall weight loss.
Based on your BMI & strong bony structure description, 135-140 pounds weight range is acceptable.
Based on observation over last 20 years of medical practice, I suggest-
1. Slower weight loss @ 1-2 pounds / week
2. Good skin care regimen (growth factor, retinal, hyaluronic acid, anti oxidant, & medical grade SPF) & skin tightening procedures
3. Under eye fillers, fat transfer or PRP may be used to address your fat loss / hollow under eye
4. A high quality medical grade eye cream
5. Collagen supplementation may be helpful
6. Worth addressing micronutrient deficiency (supplement with Omega, multivitamins, skin & hair vitamins containing Zinc, Avocado or Olive oil)
7. Collagen boosting fillers like Sculptra.
8. Consult a make up artist in your area regarding how to soften the hollow under eye.
Wish you the best on your weight loss journey!