I was lucky enough to be able to move to an office that had a private bathroom when I returned to work. There is only one on our campus and it just so turned out the person who had it quit over the summer and I was moved in there before I had to be back in the fall for school to start.
Trust me, a school bathroom is the last place you want to be changing out a bag. A space used by a few hundred nasty ass teenagers a day? No thank you.
I think that having your supplies and routine down is the best way to handle it. I went to a two-piece system because I didn't want to deal with having to empty/drain. I did learn quickly that having a drainable bag was smart for times when you have to release air because doing that from the base plate can be risky business.
I kept a cache of supplies in the bathroom including:
Gloves - It's just cleaner in general - no poopy fingers.
Stoma wipes and deodorant in individual packets - no opening and closing a big pack in the bathroom / less germy. Stoma wipes really help with wear on the skin if you do a full change, but also to clean the baseplate off well before putting on a new bag. Toilet paper was too abrasive for me.
Baseplates already cut to size and new bags - kept in their own zip lock bag to keep clean. No need to deal with scissors.
Little trash bags to toss everything in and tie off to keep the trash can in the bathroom from getting nasty.
Paper towels, already there, to lay out my supplies on.
Finally, a cooler with a six-pack of beer and a bottle of Valium: just kidding, but that would be funny.
I also kept a full change of clothes in case of an accident.
I also had different mini-packs of supplies in different places. Like my car, my computer bag, my bestie's office. Finally, I had a small purse with supplies that I carried when I left my office for lunch, went to a meeting, taught in a classroom far from my office, etc. for just in cases.
I want to say that for a long time I was embarrassed by my ostomy. Mine came from an emergency surgery after my resection failed. I had very little time to process I would be waking up with one right before they put me under. I was super yucked out by it and changing it was so nasty to me, I didn't want to look at my body anymore. I'm post-reversal now and still working on that with all my scars and the adhesions I can feel under my skin. That's another story for another day though!
But I finally got to the point where I was totally okay with it. If it hung out the top of my pants when I reached up to put my hair up I just didn't care. If I saw a shorter shirt that hit at the top of my pants and I loved it, I bought it. It didn't matter to me at all if my bag was visible. It became more about me just moving through my life than worrying what other people would think about my bag.
I let my coworkers know what was going on when I got back from medical leave so they would know why I might suddenly have to dash off. Or if they saw me without my supply bag or my water bottle to help me remember to always have that on me. Plus, this meant we could send poop memes to each other via text during meetings. Picture if you will the dreaded icebreaker activities... I would sneak to the bathroom and text my friends saying "if only you had a colostomy you could be hiding in the bathroom checking Instagram because everything assumes you have to attend to your bag."
When I got back in the classroom I let the kids know they might hear weird noises from my body and the best part was that even if it sounded like a fart they were safe because it was trapped in my bag. I also let them know if I had to dash out to be on their best behavior until I got back. They were surprisingly curious so I told them all about it and why getting a screening at 45 could save lives.
Basically, my situation was totally normalized at work and it made it so much easier for me that people knew what was going on vs me being stressed to hide it. People didn't look at me any differently and then as everyone has goldfish level attention span/memory it quickly became a non-issue. It was like nothing was different about me.
So good luck going back! I know it's scary, but I promise you'll be great!