W.P.
I can't have fun unless I'm comfortable, either. At my age (48) I'm so beyond being uncomfortable just to look 'fashionable'. You can definitely wear leggings with a tunic and cute boots (preferably flat or low-heeled). Whether or not it's too casual depends on the sweater/tunic, how you dress it up (belt, jewelry, scarf, etc.) and exactly where you are going. You could also wear 'dressy' jeans (dark wash) or soft/comfy dress pants with comfortable heels or boots and a blouse & jacket or sweater combo. (Now I see you're in AZ, so maybe no jacket or sweater over the blouse.) Sometimes it's not exactly what you wear, but how you wear it that matters most. Let your personal style come through, and chances are you will feel most comfortable. Whenever I feel clueless as to what I should wear, I look at websites or catalogs for ideas; then I tear through my wardrobe looking for similar items. Sounds like I'm a casual girl like you. My normal 'style' is Lucky Jeans & Boden type stuff, but sometimes I can dress my own favorite stuff up by accessorizing. Good luck! Have fun!