Here’s an exercise for you guys:
Play a full chord, for example a full C major (all four strings are fretted -5433) as you would normally play it.
Now play the C major WITHOUT your thumb.
I use very little left thumb pressure. It’s your right forearm than pulls the uke towards your body while your left fingers pull onto the fret board. Think of a swing that pivots on your waist/chest, and with the strap you should be able to take you left hand away and the uke will stay there in the same position.
Play full chords without your thumb for five minutes. Pressure on the fretboard, pressure on your right forearm. Now play individual notes, the C scale, NO left thumb.
It gets easier and in time you’ll wonder why you ever let that thumb slow you down.
-and get a strap on that ukulele and think about your whole body, hold that uke like you’re ready to do something!
oh and remember that this is just an exercise, as long as you can do the exercise you can go and play however you like afterwards.
Good luck.