I have never regretted buying my house in France, which has doubled in value over the last five years.
It's pretty safe to assume that what has doubled in value is the house, not France.You never know. Round bases may be the in thing this year.If I am right, then this sentence is illogical because a round base normally cannot do much in making your room decor stylish. Am I right?
Seriously, the sentence you have created is clumsy. It really needs to be:
The vase in black, which is a stylish addition to your room decor. features a round base.
I'd say more simply, "That black vase with a round base is ..."