Today I have been searching for components. Took a while. Here is the selection:

• High voltage step down converter: LMR14206 made by Texas Instruments. Its maximum input voltage is 42V, it switches at 1.25MHz and outputs 600mA. It also has  a small package (SOT23-6) and a low component count: one ceramic input capacitor, 2 resistors for feedback, one bootstrap capacitor, an electrolytic output capacitor and, of course, an inductor. 15uH is the recommended value, also confirmed by calculation.

• 3.3V LDO: NCP705. Provided by OnSemi, this tiny regulator is low-noise, low Iq and high current (500mA). Did I mention it is tiny ? It's only 2x2mm. I hope it won't be impossible to solder. The price certainly got me convinced: only 0.85$. And it also has an Enable input. I obviously got the fixed 3.3V version.

• LiPo charger: BQ24072 claims to be "USB-friendly". After reading the datasheet I understood why: it regulates its input current to avoid bringing down the entire USB power line. Long story short, if you set it to charge with 1A but you plug it in a 500mA USB port, instead if drawing 1A to fry your port, it will reduce its current to keep the 5V line up. I initially wanted to create the battery switch-over with diodes, but it won't be the case anymore. This chip includes PowerPath circuitry. If you feed it with 5V, current will go to your load and also to your battery, so you can turn on your toy even if the battery is completely dead. The circuit takes power from the 5V line, but if removed, it automatically switched to battery power. A tiny 1s LiPo UPS for just 3$.

• Micro-controller: STM32L072KB caught my eye instantly: ultra-low power, small package (QFN32, 5x5mm) USB bootloader pre-programed and low power analog comparators (there's a catch here...). Might be a bit tricky to solder, especially with the exposed pad beneath, but I'll take my chances with a hot air gun.

• GPS: of course it would have been easier if I searched the internet for "world's smallest GPS module" but I had to take the long path and search at multiple manufacturers. Many had small receivers, but only one included a proper antenna on top. Hornet series from OriginGPSis made up of various modules, but the ORG1510 is the only one that communicates using 3.3V levels. All others use 1.8V. I selected the ORG1510-MK05, because it was the only one in stock. Fairly pricey. But small: 10x10x6.1 mm.

• Finally LoRa: RFM96. Not the cheapest radio module out there, but Andreas Spiess' post convinced me. From his video, line of sight is very important for long range LoRa transmissions (for any transmission, in fact), and, as my locator will be placed in drones and gliders, it won't be a problem. Found it at the same supplier I got the GPS, at 13$.

• And of course, lots of passives: I will use 0402 components where possible. More of those after the schematics.

Having my components, I can start working at the schematics. Bye!