Straight line dress with petticoat?

You could always order one off of amazon, they’re fairly inexpensive and if you don’t like it returns are pretty easy.

You could also take the dress to a store like davids bridal that sells slips and see if they have one that you can try in with it.

Totally do a petticoat!! It will make it look so much more full. Mine is an a line gown and I am wearing it with a slip. It looks almost like a ball gown with the slip. Just a little smaller. It’s so pretty. Do it! Without the slip I feel Like a lines look flat and I didn’t want mine forming my waistline. I would not go with amazon. I bought two on there and both were terrible. Look on Mercari or marketplace for an a line slip. Here is my dress with the slip under it.

Either way it will look good! It's a gorgeous dress! Do whatever you want! If you're feeling more poof then go for it!

Your dress is more straight than what I think of as an A line. I don't know that a petticoat would look good under it.
I wear mostly vintage inspired dresses and so I have to use petticoats at times to get the full effect of the skirts. If there's isn't enough gathered skirt, the petticoat just makes me look like a compressed cone, instead of a flowy princess.
It wouldn't hurt to buy one somewhere inexpensive and trying it though, I just can't imagine that it would make your dress more beautiful than it already is.

View Quoted Comment Your dress is beautiful! I’m pretty sure that’s the same one my best friend just got!

View Quoted Comment Yes you’re right! I do think it’s more straight than anything. I definitely don’t want it to look cone like! I actually have a bridesmaid appt tomorrow so I asked my store if they could let me try on the sample dress again with a petticoat (mine isn’t in yet) so I can see how it looks! I also had no spanks or anything under the dress when I tried it on the first time and it was 6 sizes too big so it wasn’t fitting exactly like MY dress will. Thank you so much!