Hey, if you are not qualified or currently in training this type of query is very difficult to give any useful advice or at least the kind of answer you are after.
As a trained professional myself, any product I would personally recommend you are not going to be able to buy as you need a qualification to buy pro products. I have no experience of, and it is against site rules to recommend, anything you could buy without a qualification!!
In any case the reason why you are having problems could be down to any of a hundreds of things, not simply the brand of tip you are using. For example two of your complaints re: shape and strength are down to the nail technician not the tip.
I honestly don't even know where you would begin in correctly fitting a tip without having hands on tuition about sizing, tailoring and blending. Maybe you could pick this up watching another technician work but without understanding how or why she is making the file movements it'd be a bit hit and miss!!!
If you are serious about creating beautiful lasting enhancements and working safely so as not to damage your nails or develop an allergy or respiratory problems there really is no option but to to enroll in good quality training.
Hope this helps a bit explain the issues you have been having. Maybe you will take on my advice and become a fully fledged nail geek, many of us started just as you did by attempting to do our own nails and realizing that there is much to learn (and the learning never stops!) in any case, Good Luck!
