I recently had troubles with a painful muscular inflammation. Using a massage roller did help, but the roller I had was tiresome and clumsy to use. It had a uncomfortable handle that made my fingers cramp up. What I wanted was a massage roller that would fit in the palm of my hand and would not require any grip strength. The result is the device in the pictures. I am quite happy with the result.

I can not stand things that squeak, so I used ball bearings for the roller wheels. I had ssl1790zz (9x17x5) bearings laying around, so I used those. That worked out great, but ssl1790zz bearings are ridiculously over specified a massage roller. To keep cost down I made alternative versions of the STL files for cheap f608zz (8x22x7) bearings. I haven't printed this version, but it ought to work.
Search for f608zz on eBay and you will find a lot of options. Some sellers try to pass off regular 608zz bearings as f608zz, so check that there is a flange at the top of the bearing before you buy.

Everything is snap-fit. No glue or screws are needed.

I made three different wheels that fit within the shell. The curved wheel is printed as two parts that are pressed together. The other two wheels are printed as single parts.
The bearings are just pressed into the wheels. The fit should be tight. You will have to clean the hole slightly before pressing the bearings into place.
The shell consists of two identical shell parts that snap together around the roller and hold it in place.