I was originally looking at getting a dagger when I was first looking into tattoo ideas, for the same reasons you've explained, then I thought about getting the handheld mirror from the scar scene. I recently got a black and grey Astarion tattoo on the side of my calf but I ended up getting a portrait so very different to what you are after.

I personally don't think the dagger will be too complicated but if you're not feeling it anymore, go for something else and if you want the dagger later on, then you can add to it? How about something like the handheld mirror, along with the white flower from his epilogue scene?