There are many ways you can help wildlife, and you don’t even need a garden to do that - simply having a window box planted with flowers and a shallow dish of water can make a huge difference.
You could add a solitary bee box, bug hotel or bat box to your wall. But, mostly importantly… stop being so tidy! Let areas grow wild, pile the leaves and dead branches in a hidden spot and, every now and then, stop and look around - you will be surprised at how much life is around you.