I have had the Momentum Free for about 1.5 years now. If you really do have problems with small ear canals, I would recommend other headphones that use foam instead of silicone for fits. This way you can fit them better to your ear canal, they seal better and they also hold much better.
Unfortunately, I can't find any Bluetooth headphones on Digitec.ch at the moment. However, if wired headphones would also work, it would make sense to look at FiiO or Shure. There are definitely other brands with foam fits, but you'd have to look online yourself.