1) Gravity pot (like:
these or
this. These devices work by having a trigger at the base to allow the brewed tea to separate from the tea leaves when placed atop your mug. Usually made out of plastic, you can add water, heat in the microwave, then add tea leaves. This might be your best bet for an office situation.
Downsides: They can be somewhat of a pain to clean, the mesh filter at the bottom will usually wear out and need replacing after a few years, and the gasket that controls the flow of water will eventually give out on you.
2) Mug with infuser basket (like:
this, or, alternatively, your own mug and a device like
this). This can be a bit more convenient as it eliminates the need for a separate brewing device. If you go down this road, I'd suggest getting a plastic filter basket as stainless steel is not microwave safe.
Downsides: You'll need to place the wet filter basket on top of something. Most baskets come with a lid, which double as a resting place.
3) Tea straw (or bombilla). This is kind of a novelty way of drinking tea. It's as simple as putting the leaves in the mug, hot water over the leaves, then drinking through the straw. This honestly won't work with most teas, as they'll over-steep before you can even attempt to drink it.
4) As has been suggested, French Press (these are pretty universal, so I won't bother with links). This is my go-to tea brewing method for almost all cases. You will not deal with teas finer than the filter in the press, so there's no need to worry about tea passing through it. If you want to be able to put it into the microwave, make sure you get a french press that has a plastic holder. When I started out typing this list, I was initially going to dissuade you from getting a french press. But having thought about it, if you can find a microwave-safe french press, I'd go with that.
There aren't many good electric kettles that also allow for brewing. Many kettles look like they would facilitate it, but the filter at the spout is usually to help prevent scalding.
Now, for my ideal setup: variable temperature electric kettle (my one is
this Adagio model, which has been great, but I'd spend the extra money to get a kettle that can be set to a specific, numeric, temperature and not a general temperature via a dial), French Press, and mug of choice (I have this BALLER stainless steel tea cups. They are BALLER.)
] and nothin' else. On occasion I'll get vanilla rooibos with a little bit of steamed soy on top. Vanilla rooibos is sweet already, so I don't need anything else.
