I have used this one every day for 4 years, it is really nice and simple (no internet/bluetooth etc just an old school clock with a light). Great min brightness, great max brightness, and has a good 40+min gradual fade from min to max. I've tried other ones as well but they didn't work quite as well as this one.
https://www.amazon.com/Philips-Wake-Up-Simulation-HF3500-60/dp/B00F0W1RIW
The only downside is the beeping, which can be fixed in 5 min by drilling a tiny bit right in the center of the speaker hole on the back. So many people do this, there's a youtube tutorial for it somewhere.