Congrats on learning how to swim. Welcome to our underwater world.
In looking at your stroke, I never see you start from a balanced position. When you do the superman drill do you float? You are quite lean so you don't have a lot of fat to help lift your legs. That means your technique will have to be really good to get your legs up. Technique issues I see that make it harder are:
1. Reaching hands to the surface. When you extend your hand forward, allow them to drop down 6 inches or so. It looks like your shoulders are a bit stiff so your current surface level reach looks like it is straining your shoulders and pushing your hips down.
2. Your head is up (looking forward) much of the stroke. We humans like to see where we are going, but we don't get to in the water. Look straight down while kicking and gliding and only slightly forward while breathing.
3. When you do stretch forward, put just enough (about 10%) effort into lengthening your body from fingers to toes. This will help connect your upper body to your hips so the changes you make to your upper body can affect your hips and legs.
Let us know how it goes.