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
Only KN95 product I'd recommend from Amazon is the 3M 9502+.
3M 9502+ -- Be sure the item you are buying shows ships from / sold by Amazon.com. These are also available from Stauffer Safety and Global Industrial if you are concerned about sourcing PPE from Amazon.
If you want consistent quality from a KN95 product, stick with products that are audited by LA Mark, which is a quality control organization. You can use Chrome and/or Google Lens to translate as you click through the site if you are not familiar with the language.
Here is LA mark's certification document for the 3M 9502+
Note that KN95 is a self-approved specification, and is not handled by a central authority with statutory regulatory powers like NIOSH N95 in the USA. Buyer beware, especially of export KN95 products.
This product is also a NIOSH approved N95 respirator in the USA, meaning it is also audited by NIOSH. In Korea, this product also carries KMOEL-2017-64 approval. The Korean version can be had via GMarket -- only difference is the box, which will arrive with a KOSHA KMOEL approval sticker affixed to the box. Price is also better, which may be offset by the high cost of shipping from Korea. For more than a few boxes, things change in your favor.
You might also consider simply sticking with domestic NIOSH approved N95 products -- better availability.
The 9502+ is my daily wear. Originally an LA marked KN95 from 3M China, this unit gained NIOSH approval as an N95 respirator early in the pandemic.
Also approved in Korea as a KMOEL-2017-64 occupational respirator.
Low breathing resistance and great filtration per CDC testing as part of the international respirator assessment program.
Also available via Amazon.
ETA: Also a fan of the 3M VFlex 9105, which has the lowest breathing resistance of 3M's non-valved N95 options... And happens to also be one of the most economical options.
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.