BBT help!

Francesca • I`m 31 and TTC #3with my fiancée! Lots of losses 😔 my first arrived at 29 weeks, after five years of trying, our second arrived at 34 weeks, so praying for a healthy third and final addition to the family!
Does anyone else do this? I bought a thermometer that does it properly and took it yesterday but forgot today before I stood up! Does it absolutely have to be as you wake up after a three hour straight sleep? My daughter still wakes up a lot in the night so three hours beforehand in never guaranteed! Any advice?