Suggestions for endometriosis

My boyfriend is very blessed & rather large.  I have endometriosis & im pretty tight!! Needless to say having sex is very painful at times. Laying on my back hurts worse trying to get his penis in & sitting in his lap makes it easier but we are both in awkward positions. Any suggestions on getting it in easier or other positions we could try without a lot of lube?? We struggle almost every time & it's so frustrating!! I please him in other ways but it would be nice if we could do things naturally. Any help is greatly appreciated so thanks!! :)