Step one: find another job.
Do not omit step one. The fact that you will be unemployed when you leave is the biggest thing giving your current employer leverage over you. Remove that leverage.
several people have left recently, so this won't reflect well on them either
I assume you mean that a pile of people leaving all at once does not reflect well on middle management. That's good; it shouldn't reflect well on them. It should indicate to upper management that middle management has a serious retention problem, which they do.
how would you suggest I deal with this situation, to make it as bearable as possible?
Again, do not skip step one.
Step two: remove everything from your office that you wouldn't want to leave behind and take it home.
Step three: write a letter -- it needs to be in writing -- that says "Dear Boss, I am resigning my position at FooBar Corporation effective two weeks from today's date, the 31st of Frobuary. Yours sincerely, Marcus T. X" and give it to your manager, preferably after you've been paid your most recent paycheck.
If they ask you if you have signed an offer letter intending to work elsewhere, do not lie. Some companies will escort you out the door if you have signed an offer letter, because you are now both a security risk and a morale risk. This is a perfectly reasonable and sensible thing to do, and they would be wise to do so. That's why you took all your books and photos home before you resigned.
If they ask you anything else, like who you are working for next, or whatever, and you don't want to answer, don't answer. It's none of their business, and what are they going to do, fire you?
If they ask you to sign anything, do not sign it. Some companies will suddenly "remember" that oh, we forgot to get you to sign this non-disclosure, non-compete the day you started. You would be very foolish to sign it.
From previous experience I have seen they do not deal with this well, taking it personally rather than being professional, interrogating people and making their last weeks generally unpleasant.
That might have something to do with why they have a retention problem. Feel free to mention that to human resources on your way out the door.
If they make your life too unpleasant, you can always just leave.
Spend your last two weeks modeling good behaviour, documenting your work for the next person, training your replacement, and so on. Again, if they ask personal questions, the right answer is "I'd rather not discuss that". If they're mad, well, they're mad. That's their behaviour; the person whose behaviour you control is you, so behave professionally.
It's unpleasant to quit a job, particularly if management is going to be unprofessional about it. But you say it has happened a lot lately, so hopefully they will get the message that first, this happens, it's business, and second, that if they want it to happen less, they need to up their game.