Sweaters are pretty nice things to own; I would suggest buying some! Solid colors in cotton or wool are classic and will last. Oversized sweaters, cardigans, and slim-fitting turtlenecks are in style. Black is the most versatile color.
I think you should have more than just short sleeves and jackets. Most jackets have slippery linings that will feel cold on your skin. When it's really cold, you need more layers, and a sweater works great under a jacket. Then if you go somewhere that's too warm for a jacket but too cold for a short-sleeved shirt (like maybe in the car on a chilly day), you can take off the jacket and still have your sweater.
I would suggest these brands, from cheapest to most expensive:
Screen printed tee shirts are far superior to digitally printed garments. Direct to garment or DTG, is a relatively new technology. It is a great method for smaller print runs with many colors in the image. With DTG there is very little set up or “pre press” to do. You simply send the image file to the garment printer and that’s that. The quality of the print will vary from machine to machine and operator to operator. But for small quantity orders where there is a complex multi color image, it is an economically feasible option.
Screen printing on the other hand has a lot of pre press activities and tends to only be practical on larger print runs. If you print a 1 to 3 color design, screen printing can be feasible. But when you want to print 5 colors on 12 shirts it becomes extraordinarily expensive. Screen printing is best for larger print runs in excess of 36 pieces. A 1 color print may be done easily on much smaller orders but most screen printers have a 1 dozen minimum order per color being printed.
In the end screen printing will give the better quality print, more vibrant colors, and it will have the best durability or longevity. It will be the most cost effective method on decent size print runs. DTG will be easier to do, much faster to set up, easy to do small quantities, and the color is very good when done right. The longevity or durability is still a matter of question for me. But proponents will argue it is just as good as screen printed garments for durability.