can i connect my sony smart TV via thunderbolt port for better resolution.

You can connect the TV via the Thunderbolt port. However if the result is "better resolution" would depend on what resolution you have now (I'm guessing you mean with the HDMI adapter?)

I'm myself connecting the Mini Mac with a Thunderbolt->VGA adapter to my TV and get full 1920x1080 resolution.

Have you checked your Display settings? Make sure mirroring is off, then check what resolutions you can get on the current connection.

Please return with some more data.