You can inject with #29 0.5ml 1/2" insulin needles and these can be had without Rx in most jurisdictions.
"Gold standard" is just the old method. Injected T is 100% absorbed SC or IM. SC has smoother delivery = steadier levels.
You can inject into fat over your upper leg where you are relaxed, seated and can see what you are doing. There is no need for a lifetime of muscle damage.
Please read the protocol for injections sticky. The advice for new guys sticky has many technical definitions that you will need to know and other good stuff.
When you inject, the smaller the needle is the more comfortable it will be. The needle going into muscle actually has very little sensation. Your skin has many more nerves and that is what you will feel either way. If you hit a vein, that has a definite hurt and the sensation is spread out, you really don't notice that the pain is local to the injection site. When you inject, try to visualize veins and avoid.
Some find that SC injections work better in belly fat VS top of the leg, others the opposite, so you need to find what you prefer.