Hi Pinky,
There are a few things that might work in terms of muffling the noise. One would be to turn on music or a white-noise machine, if either of those things won't arouse suspicion coming from your room at that time of night (for instance, lots of people use white noise to help them sleep, so if you want to masturbate once you're in bed, you could say you've started using it for that reason). Another would be to try and mainly use the toothbrush under the covers, because that will help muffle the noise. Do any of those sound doable?
In terms of finding other ways to masturbate, that's certainly something you can experiment with! This article has some advice on different things to try:
Going Solo: The Basics of Masturbation. And, this one has some advice on things that might be similar to the toothbrush but quieter, as well as help on making sure you're DIY-ing your sex toys safely:
D.I.Y. Sex Toys: Self-Love Edition