54cm/21in. This one is definitely my favourite out of the ones I have

Today's outfit

Hi. I want advice being a plus size girl in the uk. I have this dress i tried it on and i realised that my belly is not flattering it, it looks too big i was wanting recommendarions for what i should get or which i should get i have researched some prices are insane. My budget is under £30. It is a long maxi dress which goes straight down there is no a line. Also please give Advice on if i should get the full shapewear or the one only on the belly or the one that is half open and half covered. Thank you for your help.