@francis I think the eQ-3 Max! product line is recommended in this forum as it is relatively cheap and it is known to work. Considering your setting (as you say radiators are all within a 10mt range from the BT dongle) the bluetooth setup may work fine for you, but I won’t bet on this. If you give this a try please let us know about your findings. Maybe you can start off with single thermostat and test the connectivity in each room for robustness.@rrooggiieerr might fit in here regarding the integration with pimatic as he is currently working on the BLE integration for different device types (smart tags, Xiaomi Mi plant monitor).
As said earlier you may also want to have look at “Homematic IP” which is more expensive than Max!, however.