The Bajaj Pulsar N160 is an excellent option in the 160cc commuter class and will make for a good step up from your SP125. In a similar vein, you can also look at the TVS Apache RTR 160 4V, which has similar performance and will also return good fuel economy.
Both the Pulsar and Apache have manageable seat heights (approx. 800mm). It should help you get comfortable with these quite easily after a brief adjustment period.

