Start with the Aura 9210. The Aura is a small to medium sized unit that fits a wide range of faces, but is not well suited for large faces -- so those "under medium" are good candidates to start with this respirator. Note the Aura is also available in a valved version that will be less stuffy to wear, although at a higher per-unit cost. Note I do not recommend the Aura 9205, since it has flimsy, delicate elastic straps that provide less tension and durability, reducing fit factor and reuse potential.

Another possibility for an under-medium face would be the Gerson 3230; these have a different face profile but are similar to or perhaps slightly smaller than the Aura.

If you prefer a vertical flat fold, the 3M 9502+ is a possibility as well, but depending how small your face actually is, may be on the large side.

Another potential option for under-medium faces is the Kimberly Clark Kleenguard 3400 series, which is available in both a non-valved and valved version. These are a bit smaller than typical molded cup style respirator, and also offer a full face seal and adjustable headbands for highest fit factor.

Whatever you do, stay away from anything with ear loops if you are trying to protect yourself. Ear loop devices are unlikely to seal. No NIOSH approved N95 products use earloops.

https://www.hse.gov.uk/safetybulletins/ear-loop-respirators.htm

It's all about fit and personal preferences, but...

In terms of N95 respirators, some of the better current ships from / sold by Amazon.com options are:

3M 9105 | 3M 9211+ | 3M 9205 | 3M 9502+ | 3M 8210 | 3M 8511 | Moldex 4200N95 | Dräger 1750

EDIT: fixed Dräger link -- I added marketplace codes for ships from / sold by Amazon, but Dräger sells directly through Amazon like Halyard and BNX (Accumed), rather than Amazon being a distribution partner like their arrangement with 3M... So I needed to use Dräger's marketplace ID on the link.