Welcome aboard!
A shame to hear that the feature you're after didn't come factory on your particular vehicle. My Corolla has a feature that it came with from factory which is similar to that, whereas it locks the doors automatically as soon as I reach 20kph (12mph). A great feature to have - Although it scared the crap out of a female hitch-hiker that I picked up one day
I'm sure you'll have many trouble-free years of motoring with your Rav4. There's plenty of help available here if you need it
Enjoy the forums!