Seeking andro fashion advice

I'm dating a wonderful beautiful, very femme and fashionable lady who always looks put together and amazing. I, on the other hand, am not so inclined. I'm a jeans and t-shirts/jeans and flannels kind of gal who presents androgynous to slightly masculine of center.

She asked if I would be ok with dressing up for dinner tomorrow night because it's something she loves to do and I said yes absolutely because I also enjoy dressing up occasionally, and I think it will be fun and make her happy. The problem is, I'm very recently out and all my fancier clothes are from when I was "straight." (mostly dresses) They still look good on me, but I'm ready for a new style. Problem: I don't really know what that style is.

So, fashion raptors: I'd like to get a nice outfit for dinner with my lady tomorrow night. I'm small, androgynous, and have been told on many occasions that I look like Peter Pan. I strongly prefer pants to dresses, but am otherwise open to suggestion. Do you have any suggestions of what I should look for and/or where I should look for it?

Thank you!

Edit 1: I'm in the US.
Edit 2: I welcome suggestions for something quick for tomorrow night, as well as for the future!