'which he bought' is correct and usable in written English.
For example, you could use it in a sentence such as: "He lost his book, which he bought last year."
The choreographer David Dorfman drives a Saab convertible, which he bought in his early 50s.
The put enables him to sell the stock at the price for which he bought it.
McEwan's house, which he bought in 2002, does not yet have a plaque.
Gottscho was interviewed at his home in Jamaica, Queens, which he bought in 1918.
He has tracked down Szyk's descendants and the artist's archives, which he bought.
TC Farries, a bankrupt Scottish book distributor which he bought in 1996, has returned to profit.
Yusuf Yesilova put his life's savings into the building, which he bought just last summer.
His home, which he bought for more than $1 million 12 years ago, is gone.
CCTV is being recovered from Flatley's mansion, which he bought in 1999, as part of the investigation.
Among Lumpe's fifteen thousand LPs, many of which he bought secondhand, were about five hundred of murky provenance.
(He carries Benadryl dissolving strips in his wallet, which he bought en masse before they were discontinued).
