For the last 3 years before menopause (which I happily referred to as "graduation"!), I had very heavy periods during 3-4 days of my cycle. I used 2 tampons side by side (the regular or super, depending on how heavy things were), and Kotex ultra-thin overnight maxis with wings. The absorbency was better than other pads I've tried, and the pad "locked away" the flow. Worked way better than thick pads.

I, too, had to change the tampons/pad every hour or so on some days, and did pass clots. Nothing abnormal on ultrasound, just the way my body worked when I got older. I had some shapewear underwear with a cotton crotch (which fit better around the thighs than regular cotton), which I used just for my period. It helped a lot with keeping things contained. As for public restroom use, I kept a spare pair of underwear in my purse, and also a pack of recloseable moist wipes. You can dispose of the wipes in the same container as used pads. That way, you can clean up "down there" and on your hands a bit before using the sink. As for your period taking you by surprise, the Kotex ultra-thins were comfortable enough to wear "just in case".

And BTW, disposable underwear similar to Depends come in all different brands and shapes and sizes. It took me a while to find the right ones for me, as I had to start using them a couple of years ago due to bowel and bladder incontinence from MS. I find that if I wear shapewear or regular cotton briefs over them, I feel more comfortable and no one can really tell I'm wearing them. Good luck!