Maybe a smaller guitar could help.

I found that practicing the chord form, when I didn't have a guitar in hand, was helpful. I worked at first conceptulaly picturing the chord in my mind while I was doing other things, like watching tv, listening to the radio, or any time I had the inclination. Then I worked to get my fingers to grab those shapes in the air. Just concentrating on forming my fingers into chord shapes. Lastly I started playing them on the fretboard.

I think the air guitar pratice got all the other stuff (holding the strings, holding the right strings, not muting the wrong strings...)out of my way. This allowed me to focus on the muscle memory that formed the chords. You need this muscle memory to be able to change chords quickly. In fact you need to be able to change your finger positions in the milisecond between chords, so that your fingers just land in the right place. You brain is not the right neuron group to depend on here. You need to get your spine on board. The above exercise helped me with developing this skill.