I use this and it's the only thing I've used. Look up flexible medical mirror or a variation of that on Amazon and give any of those a try. I also use a plain shower mirror for inspections of the goods ;).

Sammons Preston - 41942 Flexible Inspection Mirror with Magnifying Mirror, Multipurpose Extendable Mirror Aid for Self-Cathing, Hard-to-See Areas of The Body, Toolmakers, Machinists, Medical Patients https://www.amazon.com/dp/B071NLK3YH/ref=cm_sw_r_apan_glt_fabc_8890625BNJSD9EN3A5KD