Your best bet OP for dull tired skin would be to have a great daily routine at home - you already use sunscreen, which is great - you could add a retinoid product to your routine (at nighttime). I would recommend prescription strength tretinoin, which you can get from subscription services like Dermatica, Skin & Me etc. It really helps with skin tone and texture, improves fine lines, dullness etc. It is a slow game, you need to build up use and you may have some irritation at first, but I think it's the best thing you can use to improve the look of your skin. Just make sure you are using a high SPF daily.
Unfortunately, the sagging and double chin are tougher to fix - they're a combination of facial fat loss and general laxity in the skin (basically getting older). No cream is going to reverse this, and even salon procedures like radio frequency, lasers, peels, micro-needling etc. may only offer a temporary, subtle improvement. They will definitely give you an initial glow, but longer terms results are not guaranteed.
They generally work to increase collagen production (by creating a controlled injury in the skin, which triggers your skins healing response), but this will only last for a while, so really you need to keep getting it done, which is expensive. That's why a retinol product applied regularly is great, because over time in increases collagen production in your skin (which generally decreases as we age).
The only surefire way of reversing sagging/ jowls is surgery. Obviously not everyone wants to go down that path. You could try a few things if you like, I would just caution against spending a lot of money on devices/ products / salon treatments that promise a lot in regards to this, realistically they have limited results. A few years ago I tried Ultherapy, and spend a thousand on it. I honestly didn't much different afterwards and the recovery was brutal. A lot of these technologies promise the world, but I'm very skeptical of them.