probably the most ethical blood to use would be your own. you need to have a lot of patience to space out the blood withdrawals without taking too much and the right type of storage to hold it all.

theoretically, you could just drain blood from multiple people without killing them, but mixing blood complicates the manifestation coordination matrix and is therefore unpredictable. many have tried and many have ended up living a cursed existence

for the more squeamish , cultivating a group of devoted followers willing to lay their life down for you is an option, though it’s pretty hard to break into the cult leader raquet, and it takes a while before people are actually devoted to you.

ive found the best way to motivate a victim into consent is to kidnap one of their loved ones and threaten to kill them if the spell doesn't work. you don’t really need to kidnap them, but it shows you’re not fooling around.