This is one very common problem! Thanks for bringing up. I make sure to pick a matching lacy camisole when I pick any light-colored top in the store. I have had this problem too. Ever since I learned my correct bra size (gotten measurements taken by experts), with the rightly fitting-bras the harsh lines do not show as much as they used to. Also, being a chubby girl I have learned a few tips over the years;
• Use seamless bras that do not have harsh lines.
• Never wear demi-bras, they do not give proper coverage and they actually make you look chubbier!
• T-shirt bras and sports bras are great under shirts/ fitting tops.
• These days there are bras specifically that are for wearing under t-shirts; they come with concealing petals to hide nipples. I really like this feature should you get wet due to unpredictable weather conditions.
• I always carry a scarf/ silk shawl in my handbag. Just in case I had not noticed the bra lines inside the house I realize after coming out, I wear the scarf around to cover up.