Sitting suggestions for a tall and inflexible meditator

I've done regular meditation for over a year using a chair and later tried to switch to more traditional meditation postures. I am rather tall at 6′4/194cm and very inflexible - can barely touch bottom of my knees. I've had some success in sitting seiza using a couple of blankets but my shins go numb after 20min or so. I've been doing regular stretches for the last month or so and hope to be able to stretch enough to do Burmese sitting in the future. Any advice on whether it's worthwhile to try to reach Burmese or should I rather focus on getting better at seiza? Any equipment you can recommend? I'm pretty sure the stack of blankets I need to comfortably sustain seiza is a lot taller than the 6 inches most zafu cushions are advertised as. Thank you very much!