Hi Nick ... first, have you seen the
Saddle Explained YouTube video on the
YinYoga Channel on YouTube? That may answer a lot of your questions.
Secondly: let's examine your intentions - why do you want to do Saddle? Is it to work the top of your things (quads and hip flexors)? If so, the Dragons or Swan can also work those areas. Is it to get a deep backbend? If so Sphinx and Seal can also do that. Is it to work the ankles and knees? If so Ankle Stretch might also work for you. As you can see - there are lots of ways to work the body so if one pose just doesn't work for you, try some others. What is great about Saddle is - it works all these areas at once!
Finally: one reason many people find this a difficult pose to get into is because they can not internally rotate their femurs very well. This prevents them from going from sitting on the heels to lying back, because as they descend, the femur starts to press against the ilium of the pelvis or the hip socket. If that is happening to you, you can try starting lying down in a windshield wiper variation: lying down, knees bent, feet apart, drop both knees to one side (say the right to start), then pull the closest heel to your buttock (in this case the left heel to the left hip) and stay on your back. This is a half-saddle variation that may be more accessible to you than the other way of coming into the pose.
You will find other options in the video.
Hope this helps!
Bernie