Inkjet transfers for white shirts can be long lasting and low hand feel (not too heavy or thick). JPSS is the best known of these. It is not "self-weeding," but when used on a WHITE shirt, the transparent polymer it transfers to the shirt is not noticeable. You can see it a bit on an Ash Gray shirt. On a Heather Gray shirt it is quite obvious. Of course, since the shirt itself is providing the white of the image (the transfer polymer is transparent), any time you use a shirt that is not pure white you shift the tone of the entire image (just like printing on colored paper with an inkjet). So if using on an ash or pastel shirt you might want to trim around the design so you don't have an obvious square polymer window. But best is not to use these on anything other than white shirts.
There are inkjet papers made for dark shirts. These papers are thick and heavy and prone to cracking. They are not long for this life. They are opaque white, like a piece of paper (and some crinkle and crackle when worn, like a piece of paper). Any area not printed with ink will be the white of the paper. In most circumstances you would want to trim away all those unwanted white areas.
As others noted, there are various laser transfers that can self-weed for dark shirts. Some require a printer that can print white, some have a sheet that provides the white. While these may be somewhat better in durability and hand feel, they are still not long for this life compared to most any other type of garment decorating method, and will have a somewhat heavy hand. Perhaps worse, the papers (and if needed, white toner printers) are expensive and are somewhat finicky to use. You need a high quality accurate heat press, not Chinese junk. You need to waste some materials testing and getting your temperature and pressure dialed in. AND you need to create your art with the limitations of the media in mind. A lot of people have failed to get all of this to work. That is not to say that the process and materials are bad, only that it is not as easy as people think, and you can't do it on the cheap in terms of equipment, materials, or experimentation/learning.
There IS a self-weeding inkjet paper, ink, and process for black garments. However, it is still under development. Early results with its related products indicated that it is even more fussy and needy of extreme accuracy and control of temperature and pressure than the existing laser papers and process. Also, materials are expensive.
There isn't a cheap, high quality, easy to learn, durable way to print on dark shirts in low volumes. It's a matter of which set of problems is least bad for your circumstances and needs. DTG, inkjet transfers, laser transfers, solvent printed vinyl, Plastisol transfers, Plastisol screen printing, water base screen printing, discharge screen printing.
