I'm familiar with two basic kinds of toe stretchers. The first kind Yoga Toes and its knock-offs. I have not tried the actual Yoga Toes but I got some "Remedy Toe Separators/Flexors" for around $7. They come in only one size. My foot size is 12.5-13 but narrow, and these seem to be ok.
(yes I have stubbed my big-toes a few times lately, especially my poor left valgused-hallux)
These stretchers are relatively big but have a nice toe-grip bar which is nice for developing the "toe-arch".
I can do it well on my right but not so well on the left.
This is the best I can do with my left big toe. I wasn't able to do this at all two weeks ago. I could lift my big toe but I was not able to get the tip (distal phalanx) to flex. After a couple weeks of practice I can do it but, it is difficult it hurts along the top of my toe. I think the toe stretchers have helped.
The second basic kind of toe-stretcher that I've seen around online are the ones with circular holes.
I got the CVS ones for about $10 and they only came in one size. They are silicon rubbery and feel like thick rubber-band. They fit tight and have less structure than the yoga-toes (TM) type of separators. They also have a narrower spacing; at least these ones do.
I like running in these ones. I practically forget about them after the first few minutes. If you have a decent toe-arching ability then they won't come off. I would like to see some of these in black with wider gaps, especially for the big-toe.
For those are not familiar with this, extending your toe raises your medial arch along that metatarsal and drives the ball of your foot down.
Then if you can hold that and get your tip-toe back down then you have a degree of control over the shape and weight distribution of your foot. I guess the toes are like little levers that control the contact patch of your foot.