The most common way to add the sense of "even" is by adding the particle 도 as you suspected. There are two ways to do it in your example, however. 1. 샤워를 아직도 안 했어 = I still haven't showered yet. (as you mentioned) 2. 아직 샤워도 안 했어 = I haven't even showered yet. #2 is probably how you would say it in most daily life situations. If you want to say it even more strongly, you can add additional particles like 조차, as in 아직 샤워조차(도) 안 했어, but 조차 is used far less frequently than the ubiquitous 도. Also, 조차 is usually limited to negative or certain special positive phrases, while 도 is used much more widely. Similarly, your second example can be said in two ways. 까지 (even including) can add strength to the simple 도. 1. 벌써 샤워도 했어 = I even showered already. 2. 벌써 샤워까지(도) 했어 = I even showered too (let alone other things). 조차 and 까지 have different nuances. * 조차 = adds one like it's something special or rare. * 까지 = adds another to a group that includes more than enough already. Other examples: - 뭐, 다 했냐고? 아직 시작(조차)도 안 했는데! = What? Have I finished? I haven't even started yet! - 일이 안 되려니까 차(까지)도 시동이 안 걸리고 말썽이다 = As if everything's colluding against me, even the car's giving me trouble by failing to start.

조차(도) is commonly used for the negative meaning of "even" I haven't even showered yet 아직 샤워 조차도 안했어. Examples, She looked natural, even when lying to her mother. 그녀는 어머니에게 거짓말을 할 때 조차도 자연스러워 보인다. I would not touch a snake not even with my pair of tongs. 나는 뱀을 만지기 조차도 싫다 I didn´t know that even you would do that. 너조차 그럴 줄은 몰랐다 까지(도) is commonly used for the positive meaning of "even" I even showered... 샤워까지도 했는데...

I haven't even taken a shower yet.. 나 아직 샤워도 안했어. 나 아직 샤워도 못했어. -------------------------------------- when your friend cancel in the last minute, 나 샤워도 했어. 나 샤워도 했단 말야. 나 샤워까지 했단말야.