I can’t do the full seated with crossed legs position, any good stretching exercise that can help get me there faster?

I would focus on stretching out your hips. You can do a lunge stretch, 90/90 stretch, or figure 4 stretch. I personally do a standing figure 4 and it seems to help. Here’s a link: https://www.google.com/amp/s/www.self.com/gallery/hip-stretches-your-body-really-needs-slideshow/amp

don't worry you're doing a great job as you are. You don't need to get anywhere faster than you are doing already. It's all about small steps making progress not actually getting there. Enjoy the process