Thank you for this great post. When you say "transition" do mean "progressive"? Transition I believe are the ones that "change" to sunglasses when you go outside. Progressives incorporate readers.
When I travel, I have my regular glasses (which are progressive), sunglasses (which are also progressives) and transition. I love wearing the transitions in situations where I may not want to carry sunglasses and having to switch back and forth between the glasses. Like maybe a hike or bus tour or something where I don't want to be carrying a lot. But, I don't love the transitions, the way they look when inside and they really don't have enough sun protection outside. I do pack the transitions as my "back up" glasses when I travel.
But, you are right, this is a lot of space for eyewear, and we pack carry on, too. I also like to pack an empty case to hold my glasses should I want to store them on the plane.
I have not seen the glasses' case that incorporates two pairs of glasses. I think my sunglasses may be too big, but its worth a try.
I don't desperately need glasses for distance. My eye doctor gave me a magnification number to look for in drugstore readers should I need a hack for distance if I lose glasses while traveling.
Another option for OP is to look into contacts. They've made a lot of progress into progressives in contacts. Also, for me, the optometrist experimented with making one contact stronger for reading so that one eye carries more of the load for distance and the other for reading. I did like the contacts a lot. I quit using them during COVID, but may go back to them.
I do like the neoprene glasses' case. It is space saving and I can clip to the outside of my purse. A downside is that I don't feel they offer enough protection and glasses could end up crushed if not mindful.
When I went to Amazon to look at the double case, I also found this one. It's probably takes up less space. I LOVE LOVE LOVE that the mini screw driver is attached. This case also could end up crushed like the neoprene, but I'm going to give it a try.
https://www.amazon.com/dp/B0FP55W32S/ref=sspa_dk_detail_2?pd_rd_i=B0FP55W32S&pd_rd_w=b94o8&content-id=amzn1.sym.8ea86d39-ba43-4d13-ab5d-eaeb53c21798&pf_rd_p=8ea86d39-ba43-4d13-ab5d-eaeb53c21798&pf_rd_r=BR5NC42BJ4MPYQD8Q9SE&pd_rd_wg=lrBpm&pd_rd_r=d69ffeb2-058e-4eed-b4b4-cb3c858c14d0&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw&th=1