Hi there an0nb4be, welcome to Scarleteen.
Firstly, with regards to your experience in your changing response to masturbation, this is really normal. Novelty can be one of the things that contributes to arousal, when that begins to fade (as all novelty does when we do something a similar way more than once) then it makes sense that we increase the other ingredients that make us feel aroused, like physical touch and fantasy material (ie. like the porn you mention). This isn't a bad thing, particularly if you find those elements pleasurable.
When you say that you're masturbating more than usual, and feel that it is linked to your depression, would you be comfortable expanding on that a bit more? Are you finding it a way to lift you mood or decrease stress? That can be a good thing, as long as it isn't keeping you from other things you want to do, getting enough sleep or your responsibilities and/or self care. Would you say that it is or isn't? Do you feel like you are ultimately deciding whether to masturbate, or is it feeling more compulsive (like you can't stop yourself from doing it)?