Greetings Tammy! Welcome to the forum! Upavista Konasana is my very favorite pose. It is probably my favorite because it took practicing every day for 1 year before I could lay my head flat on the mat. I haven’t seen Willem post for some time, so I will try to assist as best I can.
My students also have a difficult time with this as well. When we prepare for this, I have them spread their legs wide, knees pointed to ceiling and feet flexed. Towels under the knees and a pillow or blanket, as Willem suggested, under the bum to tilt the pelvis can greatly help. I have them bring their left fingertips to the front of the mat and their right fingertips behind them. You need finger strength to do this, but lift yourself off the mat and rest your bum back down. Then bring the right fingertips in front and left behind and do the same thing. Now your legs are nice and wide. Place your hands on your hips. Lengthen through the spine and as you do so, engage the abs and bring them ever so slightly in toward the lower back. Keep the upper back straight and begin to spill forward from the hips. When your hips stop moving, you stop moving. This is your starting point. It is also important to lighten the load as I call it. Don’t try to keep you bottom so firmly planted on the mat. I would try to measure your progress somehow, because this pose really does require persistence, and this way you can feel good about your progress. You can use a block that your rest your hands on and as you begin to loosen up, you can move the block away.
There is also a sequence that helps. With your legs wide, doing the same prep as I stated above, slide you right hand down the right leg and bring your left arm up and over trying to reach your right big toe. Hold for several breaths. Now turn to face the right leg and release head and torso over the right leg. Again, hold the pose for several breaths. Now walk your hand to the center and hold for several breaths and then come back up, repeating on the other side. When you walk the hand to center, most students are farther down then just going into the pose without the sequence. You can try it and see what you think.
If you have 2 people who can place their feet about 2 inches from the hip crease on you upper thigh, have them put a slight amount of pressure on your thighs. Now try to come forward. Sometimes it’s the grounding of the thighs/legs that is the problem. The top of the thigh moves toward the back of the thigh which presses into the mat.
And also, preparatory poses such as Baddha Konasana, Trikonasana, Supta Padangusthasana will help immensely if practiced daily.
I just gave you a bunch of info, so if it is confusing, let me know. This pose is soooooo worth the effort! Truly liberating!