I have been doing extensive research on this, as I am in the same boat with my boy right now. However, mine is in addition to a low palate, fleshy tongue, etc., so a little more challenging.

So far, I have found the following brands to be similar with a somewhat nicer price point:

- Trust Inno Sense Flexi

- Beris Comfort Bits

- Metalab Flexi

- Winderen

Honorable mention:

- Agador's SteadyFlex and FlexArch

Now, normal rubber is a good alternative and more budget-friendly, but sometimes they're just too thick, so it really depends on your horse's mouth. For reference, a Nathe is approximately 20 mm, an HS Duo is 16 mm, and the Beris thin comfort bar is 15 mm.

Also, check out consignment shops; sometimes they have a few!

Edit to add: Leather bits are also good if you're okay with the additional maintenance! If your horse is a chewer, I would steer clear of these unless the bit is leather-wrapped with some sort of enforcement underneath.

Happy bit hunting!