That's a good question.
Having been blessed with a shower of excellent water pressure when I was young I'd just use that. No special nozzle, no special head for it, I simply pressed the water jets against my hole and the water pressure did the rest, squirted straight inside me. Make sure you get the water temp right though. Too cold and you'll feel like you're cramping inside, too hot and that's not nice either.
If you've got a shower with a variable stream setting, the one where you reduce the stream to a few narrow, powerful, jets might do the trick. Although I tried this at my friends and the water pressure wasn't enough to get it inside me. I was quite surprised!
Beyond that get creative. I don't actually have a douche. I have one of these...
Prescribed by my doctor years ago to try and help with a nasal issue. It didn't work at all with that but I looked at the bottle and thought. Well if it squirts water up my nose why can't I sit on it and squirt it up my butt? So yeah, squirt, poop, squirt, poop until the water runs clear.
The bonus of nasal rinse bottle is that no one would think anything of it.
Another option would be to use a bottle of some sort, even a standard 2 litre one that you get at the shop with coke/water in. Unscrew the cap, use something to poke a hole in the cap, fill the bottle with water, put the cap back on. Press your hole tightly against the lid and squeeze the bottle. It'll probably take a bit of practise to find how hard you need to squeeze the bottle or how hard you need to sit on the bottle but it should work. I mean technically you could use a bit of lube and insert the lid before squeezing! Yeah it'll be messy but douching is messy, so do it sitting in the bath/shower.
And I just found this...
Problem solved. Just be careful inserting the pointy nozzle. Well I mean you can make it less pointy.