Resting is a common behavior for betta fish, and unless you see signs of illness or distress, there is no reason to worry about his comfort. Bettas like to rest on gravel, or even on plant leaves. Some do this more than others, and some may not do it at all. Just like people, every betta is different.
This is one great reason to have a hiding spot for him somewhere in the tank, such as a small cave-like decoration he can easily swim into. He can escape from the world and have a calm, dark place when he needs it. There are also products made especially for bettas to rest on which you may want to introduce into your tank, such as betta hammocks.
While a lazy betta isn’t necessarily a concern, you do want to make sure he isn’t staying in one spot for the wrong reasons. A strong current from the filter may push him around the tank, and if he is sitting on the bottom to escape it, you may want to consider finding a way to reduce the filter flow.
Of course, you also want to check your water parameters regularly to make sure there is nothing wrong with the tank water, and he isn’t getting ill.
Otherwise, if he appears healthy and happy, try not to worry if he likes to rest.