You might want to consider using a microcontroller that supports Bluetooth Class 1 power levels and the latest Bluetooth 5.0 encodings (e.g. LE coded PHY (long-range) which provides more range at the cost of speed). Combine this with a proper external antenna that has a decent gain or directionality depending on your application could help.
Otherwise, you could try using pre-amp front-end module ICs such as the Nordic Semiconductor nRF21540 (https://www.nordicsemi.com/products/nrf21540) that can amplify the output of a weaker Class 2 device to Class 1 levels.
Other than that, yes, the use of BLE Mesh will also extend range but requiring intermediate nodes to do relaying of data (which could require a steady source of power).
There are different ways to extend the range of Bluetooth transmission. One of them is also increasing output Tx power. Others are using different PHYs and some are also to use different antenna design. Consider using nRF21540 or similar if all you are looking is IC for it.
