I'll share one of the best things I've heard about notes:
The main question that any of your relatives ones may have is "Why are you ctb?" If you decide to answer it in a note, then:
Do not describe the entire decision-making process (in which arguments against suicide could be found). Talk only about the reasons why you decided to do this.
It is best if there is something as it that the survivors will be able to understand, but will not be able to challenge. And there is a way to achieve this — to emphasize your subjective reaction.
Instead of citing some event as the reason for leaving, explain the reason as your reaction and feelings about it. This is much more difficult to challenge, because someone else could have reacted differently, but they are not you. Given your situation, you had options, but you decided to choose the one that you thought was the best.
Your family may still feel guilty for not making a difference, but the situation could have been very different and you would have decided to CTB anyway, because in the end it was your decision. By describing your death as a decision, you take responsibility for your actions, whereas if your death is an event, then it's not your fault at all: it was just a deterministic consequence of your situation that only other people could change. Taking responsibility can take the burden of responsibility and guilt off your loved ones.
P.S: If I wanted to leave a suicide note, this advice literally saved me from having to write an entire bible dedicated to each of my painful experiences for my parents, which could also be interpreted in different ways.