What to wear

I'm going for my 12 weeks dating scan tomorrow and really unsure what to wear for it. When I had my ovaries checked before I wore jeans but the gel got on them and I ended up being rubbed raw and developing a rash. I don't own any tracksuit bottoms or leggings so they're not an option. I usually wear dresses and skirts but don't feel this is appropriate, would it be alright to wear thermal tights that are about the same thickness as leggings or is that also inappropriate? Help please!

My mum and eldest sister are going to be accompanying me if this changes anything. I just want to make sure I'm comfortable because I can't get changed after and may be going out for a meal to (hopefully) celebrate my sister getting the all clear after an operation to remove precancerous cells from her uterus.