I'm going to tell my ex that our son shouldn't be sleeping in her bed
Why is your son sleeping in his mom's bed a problem?
I am upset that I never got to sleep with my mom in her bed.
As long as it's not causing problems for your son you can't tell your ex how to parent your child. If you are concerned about the arrangement you should talk it out and see if she understands you point of view.
I know that it's no way right and a thing that needs dealin with. But I want to split them up by every means.
That is not a nice thing to do. You should not tell someone else how to parent. You should do things how you want to and let them do what works for them.