Artsnletters makes a good point for a smaller/lighter carry-on on a shorter trip and I'd do the same.

I too have mailed items home from trips without any issues. That said, one of DD's friends did a study abroad in Russia and the box she shipped back never made it. It had everything she had bought for people. So maybe just ship back your regular clothes, etc instead of new special items.

Even MORE depends on how often you plan to DO LAUNDRY.

For extended trips which required both business and casual wear, I have used a 28" Bag. Yes, it's big. But it's wheeled and does fit down the aisle of trains, admittedly with little clearance. I do prefer to use a smaller bag if possible, but it's not the end of the world. And, as noted, you may only need to deal with this on arrival and departure and not for any side trips during your stay.

I second the idea of a collapsible duffel - have a couple that I use all the time. They are great for gym visits or day trips.

I mix and max dirty laundry (in space saver bags) with souvenirs on my return in my checked and carry on luggage so as to maximize my allowed checked luggage weight and minimize my carry on luggage weight.