We decided to only consider GPS based on the uBlox M8. This was due their high functionality, low cost and support for high altitude working
These capable GPS units based on the UBX-G8030 IC support multiple GNSS (GPS, GLONASS, QZSS, and SBAS). With external flash, they can also support Galileo and BeiDou. In airborne mode the M8 module are capable of working to a maximum altitude of 50km
Our early development was based on uBlox MAX-M8 modules, but these required PCB mounting and were expensive in small quantities. The uBlox NEO-M8 adds a low noise amplifier(LNA) and SAW filter, and clones are available at low cost, but again they require PCB mounting. We found the following UBX-G8030 based boards with LNA and SAW which were low cost and easy to connect to without an additional PCB. They all have flash memory and battery backup.
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Beitian BN-280 The module is available with and without a compass inside. We don't use the compass and don't have an I2C interface available on the HC12, so either is suitable. The interface has six pins including the two unused pins for I2C of the compass. The unmodified module weighs 13.5g, removing the ceramic antenna and screening can gives a weight of 2.5g.
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Beitian BN-220 This is the small brother of the BN-280 at 22mm * 20mm * 6.5mm. It has an integrated antenna and a 4 pin interface. The unmodified module weighs 5.6g,
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TOPGNSS GG-1802/GB-1803 These are the smallest of the GPS modules we used at 18mm * 18mm * 6.2mm. With integrated antenna and a 5 pin interface including a 1pps output. The GG-1802 is GPS and GLONASS by default, and the GB-1803 is GPS and Beidou by default. The unmodified module weighs 7.25g, removing the ceramic antenna gives a weight of 1.6g. We might get the weight down to around 1g if we remove the screening can and the connector.
All the above GPS modules are available for around £6 each have worked for us and appear to be based on genuine UBlox chips.