Original iPhone SE is relatively easy to work on, two pentalobe screws and a suction cup will get you into it. It’s not waterproof so there’s no glue seals to warm and melt, it’s still mostly screwed together inside, only the battery has glue strips holding it in.

From there I’ve swapped the battery, moved the logic board and home button to a new chassis, taken the camera module out and tried to clean it, had the screen+top chassis off. It’s not for everyone but it’s not technically complex with many specialist tools, it just needs a battery replacement kit, tiny screwdrivers, workspace, and patience.

No, I went to a local electronics shop. I don't have a pile of decommissioned phones in my house, nor the eyesight or hand-steadiness for fixing things that small. User-serviceable is definitely a distinction, but I suspect family members would expect me to be their technician anyway, and I'd point them to the electronics shop due to physical issues above, and fear of bricking their devices.