(Be sure to get ones with a base — I think it’s important to have room for a dollop of mustard on your dish so that you can scoop some up with each bite, and they’re also sturdier and easier to stack and store)
They used to be really hard to find in the US (I originally got mine at IKEA but they didn’t have any the last time I checked). Fortunately, Amazon has a few options that seem good.
I like these egg spoons. They have a nice long handle, but are small enough to maneuver inside the shell through the opening made by my egg topper.
There are also tiny spoons at IKEA to consider (the mopsig, for example, have shorter handles, a rougher finish, but are cheap enough to stock up on).
I use tiny spoons for soft boiled eggs, but also for other foods that could be eaten in two bites, but shouldn’t: creme brûlée, a scoop of ice cream, etc.
There are so many delicious mustards in the world. If you haven't already experimented, you're in for a treat! I'm not sure if it's regional, but I'm a fan of the Sierra Nevada mustards.
Tiny salt shaker
My host family in a Germany had the perfect personal salt shakers for a case like this where you need to repeatedly re-salt as you make your way down into the egg. In America I’ve mostly just seen them on room service trays in fancy hotels. But I think it’s worth having a couple at home, just for the lovely ritual of soft boiled eggs.
(There’s a weird thing where you could get one or two for $8, but if you want a couple dozen, they’re <$1/ea. and might come with a carrier(!) — I’ve linked to the best small bang for your buck that’s also less than room service ;) and maybe you can gift your friends with “extras”)
Egg-topper — this isn't necessary if you're good with a knife and/or fine with a bit of a mess. But it's pretty wonderful once you've decided to make soft-boiled eggs part of your routine.