fair play to you for litigating this yourself (officially i'm outraged of course)
i think you probably have the correct inclination there with the loss of a work day(s) approach. you could hardly call this an "extra cost" - it was clearly a cost. if you used holiday allowance that's a day's holiday you don't have (if you see what I mean). if you are self employed then your accounts should show the average days income.
you can't claim a "professional fee" equivalent to what the other side would have gone down for if you had legal representation - you didn't use a "professional".
I'd imagine you presumably gave evidence yourself so you might actually recoup your expenses as a "witness expense". hard to see why you wouldn't be entitled to your own reasonable expenses therefore. you'd also be entitled to have had a bite to eat , perhaps a cup of coffee to keep you alert, and to some travel allowance for the particular days.