I've never had that much of a problem working with MIDI in Reaper, but I often find velocity adjustment awkward. Is there any way to set mouse modifiers so that clicking and dragging anywhere on the MIDI note moves it (so there's no way to adjust the velocity) and clicking and dragging with a modifier held down adjusts the velocity?
The default modifiers look such that alt-left-dragging on a MIDI note adjusts its velocity. To prevent accidentally adjusting velocity without the mouse modifier, you can ensure that "View: Toggle show velocity handles on notes" is off.
And to elaborate on tack's answer, check out this screenshot on where to find
the setting: "View: Toggle show velocity handles on notes" , in MIDI Editor.