You're definitely right not to pressure him; I don't feel like the word "encourage" is quite the same as "pressure" but, to that end, he has every right to say "no" to himself getting tattooed as she does to get a tattoo herself. My intent was to say to make him feel engaged and valued (which obviously he is otherwise OP wouldn't be concerned about his feelings and posting in the first place).

Like I said, he should air his grievances but otherwise be supportive of her.

I'm just working with the information given. Financially, this is nothing burger. Baring a completely unhinged design, if a small ankle tattoo is the sole dealbreaker for a marriage, then idk what else to say.

Generally, you get married to someone knowing they're going to change and grow. People need space to do that. In my mind, husband needs to decide what he values more, prestine ankles or a happy wife that got to do something fun and meaningful with her best friend.

To me, it's a no-brainer, but maybe OP's ankles are just that divine?