I'm glad that the articles Elise shared have helped you feel a little more at ease. I hear your frustration, and that feeling of being "broken" but I honestly thing that with a bit of care and taking the pressure off yourself that you'll be able to have insertive sex that feels good, if that's what you want. You've made some good points, so perhaps we can go through them to explore a little more about what's going on here.
You're absolutely right that communicating with your partner as you go is going to be important as you work towards having that strap-on inserted if that's what you want to do. My suggestion would be to bring it up *outside* the moment, to take the pressure off when you're actually getting sexual together. You've made a list of suggestions here of things to ask for - great! How do you think your partner might respond if you approach her with them? You could also ask to be the one in control of insertion - even when she is the one wearing the strap-on.
You suggested that you might not be fully aroused, or that there might be mental blocks happening. Those are two of the first things I'd want to explore in your situation. Let's talk about mental blocks first. A lot of pain on insertion happens because the pelvic floor tenses up - something it sounds like you might be experiencing? This is an involuntary reaction, but the thing is that if you learn that insertion *is* painful, your body is more likely to do that protective tensing to prevent insertion...and it becomes a bit of a vicious cycle. Some things to try are lying on your back (you can be fully clothed!) and allowing your knees to relax apart, taking some time to breathe, direct your attention to your pelvic area and notice any tension. Some people find it useful to do things like visualising their vagina relaxing, or sending their attention up into their body through the vaginal canal. Notice if how you feel trying to relax and mentally "open" in that way - does anything come up for you?
The other thing is to make sure you're really turned on before trying to insert anything into your vagina, and then starting small with loads of lube. You don't have to jump straight to a strap-on or full-size dildo. A little finger, small bullet or un-intimidating toy is a good place to start! You can just put it as far as is comfortable, leave it still if you prefer and just notice how it feels - trying to stick to what feels good and comfortable. What do you think?
[A side note, sharing toys is one way that STI's can be transmitted, unless you're using condoms on them or sterilising between uses, so taking steps to limit that transmission is always wise! Happy to talk about what that looks like