I've been lucky and always had loads of slow worms about the gardens I've had. In our current place I leave old black baking trays upside down, pieces of slate and other dark objects and there's often a gathering of slow worms underneath them and lizards use the tops to warm themselves up during the day. Plenty of long grass, weeds and a bit of old rigid fencing keeps the birds and cat off them as well.
Mowing can be tricky but I don't mow much and walk over the paths first. The mower is also on a high setting so tends to move over them.
A decent compost heap also provides a home for them.