Going on a dinner "date" and would like some advice

I am going on a dinner date this weekend and am relatively new to paying attention to mens fashion. I am a blue collar worker, who outside of my dingy work uniform, have always just been a jeans and t-shirt kind of guy. I'm 37 years old and want to change up my image a bit, and just dress better over all. We are headed to a slightly above average dinner at an Inn on a small lake and I would like to dress well but not overly. I'm a larger framed guy at 6' 210 lbs so finding decent clothes that fit well have always been an issue. and I don't think I want to wear a blazer or sport coat....it just isn't me. I like darker colors.  Any suggestions??

Agreed, I should have posted a week ago. I have been shopping for a week already but just don't feel comfortable with what I am finding which is why I posted today. As far as a sport coat goes, do you agree that one should dress within their personality as to not promote something that isn't? Just my thought but.....I could be wrong.

Thank you to the people who have posted helpful responses. There is a reason for this particular inn. It was a place that was frequented with a family member of hers that has fond memories. I just don't feel I should promote myself with a sport coat or blazer if my everyday living is not that style. We met in my work "blues" so she knows who I am as a person. I want to dress well but not outside of "me". To each their own right? :) That is why I posted here was to get some helpful hints...thanks again!!!