Still struggling to find a chastity device that fits me properly

Here is what I have purchased and tested so far:

• CB6000 (clone) - I just can’t seem to get it onto the tube, regardless of how hard I try.
• HT V4 (clone) - Same issue with me; unable to slide into the tube no matter what.
• Cobra Comfort/Large 85mm (clone) - This one works for entering the tube. The largest ring size is fine too. My cock gets sore after a few hours of being squeezed tight though.
• Cobra Max (genuine) - The tube has a bit more width initially but tapers in along the shaft. It’s UNUSABLE for my setup because I can’t get inside it at all.
• Cobra Medium 75mm (clone) - Fits slightly better than the others. When I am fully relaxed, there is less space near the tip. So far, this is a good fit for me.

I have one more possibility coming my way:

• Cherry Keeper custom model with a large ring to help reduce the “water balloon” sensation on my testicles.

Just to clarify:

• Yes, I know how to take proper measurements.
• Yes, I understand the techniques for getting into tubes and rings.
• Yes, I am aware of custom devices, but I am not willing to drop $300 on just one device.