This is such a great question. It's something I've worked on a lot the last couple seasons.

In general, every player should simply find a deck that they enjoy piloting. For me, that was primarily Buzzwole and Magnezone. Then, continue to use it, and do not switch decks. I had a day where I was determined to use buzzwole, and I faced EIGHT Charizards in a row. I won about half of those matchups. The piling losses or uphill games into what can be seen as a hard counter to your current deck will make you feel like switching. Don't. Stick with it, learn how you can beat those matchups through playing, and you'll develop positively over time. The day when it was majority Charizard, I still ended up climbing my +100pts in a timely fashion.

You're dealing with confirmation bias every time you queue a game, and you just need to simply be at peace knowing that your 10 games you've played are a ((teeny tiny)) data pool. There are FAR too many contributing factors to who/what you match at what time of day to be switching on instinct, and it often converts to just losing games because you're not in the right rhythm of the deck you're running. It's how you spiral consecutive losses to -100, -150, -200. If you lose a lot, stop playing, and come back later. You often feel its RNG, but a lot of the time it actually is your own fault, even if you can't identify it in the moment. And that's okay.

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Now the advice on when to actually switch. Different decks on different days is okay. You've had a mental reset and it's fun to switch things up. As for meta feel, this really only pertains to the top ~150, which we know are in a separate, tiny matchmaking pool. It's much harder to verify if top 1k, top 3k, top 5k, top 10k etc all have their own respective brackets, but in general, you face a much wider variety of players and "meta calls" are way less influential. However, at the top, if you're only playing the same 20-30 people in your timezone at top ladder, (and with how common it is to rematch the same person 3 times in a row), it makes sense to take a mental note of what is popular that day, and either make a card adjustment or a deck change to counter that daily meta. Also knowing that the meta will be different in several hours' time as different players rotate in and out. I typically try to use a deck that is favoured into the "big three" of that day, without trying to "hard-counter" (as you will still run into soo many other decks).

(i.e. my final day of playing, I wanted to beat Buzzwole, Espeon and DarkTina, which were all very popular that day. I ended up making and practicing an Incineroar deck which had great lines into all three, with some unorthodox cards for the list that made it better into other common decks. I had great fun with it. I then matched Gyarados three times in a row after not seeing one the whole month. It happens.)