Personal ledgible quick cipher
Teach myself an uncommon written language like Esperanto or Klingon which very few people can read


That's not a bad idea. Although if you had to choose one I'd personally advise you to use Klingon instead of Esperanto. The amount of worldwide Esperanto speakers is about 1 in 4000 (0.03%), whereas Klingon is spoken (fluently) by only 20 - 30 people.

The goal of Esperanto (as you might know) was to introduce a universal language with the intent of making the learning process fairly easy, some might even say that Esperanto is very easy to learn. Many words are derived from European languages:


  [...] took most of [...] Esperanto root words from languages of the Italic and Germanic families, principally Italian, French, German,
  Yiddish, and English. A large number are what might be called common
  European international vocabulary, or generic Romance
  
  - Esperanto etymology (Wikipedia)


It's likely that European speakers can recognize some words from Esperanto and maybe in rare instances connect the dots to gain contextual knowledge of a text.

Additionally, there are numerous Klingon &amp; Esperanto online translators (if anybody should get hold of a text).




  Replace the symbols I use to write letters with alternatives, like Elian-script


That's probably a good method. If you do this every day it should be fairly easy for you to learn reading and writing in a cipher and obviously you can invent such a cipher yourself.

However, I have to say that it's unlikely to go beyond a monoalphabetic substituition cipher. Polyalphabetic substituition ciphers are rather hard to do fast by hand / mentally for numerous reasons.