I tried this for the first time just this week. I used a kit made by Testor's I found in the toy section at the local Wal-Mart. (cost about $5) This kit comes with two sheet of decal paper. One clear and one white...both sheets are 5 1/2"x8 1/2". The kit also has a small spray can of clear overcoat...plus a CD with a worthless graphics program on it.
I used MS Word and PaintShop Pro to manipulate the graphics. Printing was done on a HP 940c inkjet printer.
The results were dissappointing. The clear sheet turned out good, but the white sheet isn't opaque enough to make the decals useful on dark colors. BUT...it was a cheap experiment...
So...you might look at your local Wal-Mart or hobby store for the decal paper.
This stuff looks promising for inkjet decals.
https://www.supercaldecals.com/
Here's a source from a "rocket guy"
https://www.tangopapadecals.com/
but I don't think his paper works with inkjet printers.
Good Luck,
John