From Current Product in Simplicity Studio, click the Parametric Search icon.

The search tool will start, so select MCU Core (M0+, M3, M4), Flash size, operating speed (MHz), RAM size, number of I/Os, and presence/absence of various peripherals. There is a ▲ mark on the right side of Flash and MHz, but by clicking this, you can switch the search condition (more than 〇 kB or less than 〇 kB?).
The device model numbers that meet the conditions are listed at the bottom of the screen.