I don't know if this is something that you've already tried, but Bookman sensei in his video on ukemi does a really neat intermediate step where the aikidoka learning to fall uses a kneeling and crouched down partner as a support. The whole fall is done very low to the ground with a lot of support. When teaching ukemi I've found it helps considerably with those who find the fall intimidating. Rather than do a poor job of describing the process I think I'll just suggest you find a friend with the video so you can see it for yourself.
I hope this is helpful,