My dear, for me the only thing that works is to allow dd to scream in frustration in order for her to get a mouth big enough to latch on. Once I could accept that this is part of the process, she began to latch. I don't like it that she screams, but it's what works for now. I expect it'll get better as her mouth grows bigger.
Good positioning helps. If you are doing cross cradle make sure the baby is up high enough. What works for me is to line baby's eyes up with the beginning of my armpit, hold body close to me with chin towards to breast and baby's upper lip/mouth further back. I have to let her fall back a little to cry/get her to open her mouth, otherwise she just licks my nipple and makes a tiny mouth. Then when she makes the right mouth I have to swiftly and firmly whisk her on my breast, chin touching breast first. Check out drjacknewman.com for videos for latching.
Do you have access to real live help? LC or something? Hang in there, it's so hard and frustrating at times. You're doing a great job.