What was the size the ark of the testimony? What was the size the Holy of Holies? I once heard that the ark was bigger than the holy of holies. Is that true?

It seems that you are referring to the Gemara in Megilla 10b. According to Sefer Melachim, the width of the Holy of Holies was 20 Amot. According to Rashi's explanation in the Talmud, there were 10 Amot on each side of the Aron in the Holy of Holies. Therefore if the entire Holy of Holies was only 20 Amot and there were still 20 Amot on the sides Aron, the only way to explain it if the Aron itself took no physical space.