One approach is to start by looking at feature you need which will help you decide what you finally want to buy.
For example with locks, do you need a deadbolt or not, do you need auto lock, do you need a privacy or vacation feature, do you need a built in alarm and so on. Here’s a post on locks to get you started on this journey:
Similarly for thermostats, do you need a Z-Wave or WiFi (wifi through third party has a dependency on cloud to cloud communications), do you need a basic thermostat and then use add on SmartApp to make it do what you need (e.g. Motion Sensor Based, 5-2 Day Scheduling, Custom Scheduling, using remote temperature sensors etc) or you need something with that stuff built in so you don’t need to depend on SmartThings.