That's a decent shower size. What size shower were you considering? If the walls are around 4 inches, replacing them with glass panels would gain you 2 or 3 inches, I imagine. Would that result in a strong enough sense of expansiveness? Especially with the window next to the shower, you'll get a lot of light in there, adding to the feeling of "space". Reversing the door swing might allow you to square the shower. (Just spitballing ideas here. Not a pro.)

ETA: A contractor told me this is not the time to consider changing windows. Something I've read here as well. Don't know when you're planning this reno.