Typing Pinyin

I've been typing Mandarin on my computers for about a year now, and have been using "Pinyin-simplified" as my keyboard to convert my English letters to Chinese characters. However, I'd like to start typing only Pinyin with tone marks. I know that if you hold down the vowel keys, you get some tone marks, but there are 2 Chinese Pinyin letters that have tones that are not present when I hold down the vowels on the keyboard. I'm not sure how to type the tones in "nǚ" and "wǒ". How can I write these tone marks on my Macs?