144k of SRAM is cutting it pretty close.
I’m not sure if the qgsm port of the Cellular Library has been tested with your particular modem. Please let us know if you are successful with it or submit any necessary patches on GitHub to get it working.
I would suggest dropping corePKCS11 from your plans due it’s ram/flash requirements (it is meant primarily for mock/testing purposes anyway). You’ll need to determine how to handle private key provisioning and storage in a way that meets your application’s security model.
In general, disabling RSA operations should save you a fair amount of ram
and flash regardless of the stack used. You might also consider an alternative TLS stack since mbedtls is not very well optimized for platforms with extremely limited SRAM. BearSSL is one such option and is used by the espressif ESP8266 sdk.