Hi Uzii,
It depends on what you want to do. If you want to do dye sub, you need to buy sublimination ink.
If you want to use heat transfer sheets with heat transfer paper, you pretty much need pigment ink.
I am currently testing
JPSS (jetprosofstretch paper for lights) with Canon Regular Dye ink. On the 7th wash, the last two washes with one cup of bleach each time, and I have not had any fading.
If you want to try and test the ink you have in your printer with
JPSS, you can get a sample pack (3pgs) for a penny (1 cent) from tshirtsupplies.com (with low shipping) to test it out. Who knows, I never thought Canon ink would hold up.
Papers for dark shirts are only known to work with pigment inks, so if you want to do both kinds of cotton shirts, you'll need the pigment ink anyway.
Best regards, and good luck to you!