How can one deal with the loss of items from the bedroom, given the suspicion of internal theft, and is Istikhara prayer permissible in this situation, in light of the Qur'an and Sunnah?

One should think well of a Muslim and strive to search for what is lost, for its loss might be due to oversight. It is prescribed for a Muslim to supplicate by saying: "O Allah, Restorer of what is lost, Guide of those astray, You guide from error, return to me my lost item by Your might and authority, for it is from Your grace and bounty." One should inform the husband's mother of the loss without accusation, maintain the household adhkar (remembrances of Allah), recite the Quran, and mention the name of Allah when closing doors and storing belongings to ward off devils.