Credit: Jean Baptiste Lacroix/

Reese is ready!

Set to wed CAA Agent Jim Toth within weeks, Reese Witherspoon has made a decision on the most important detail for the day: her gown.

The bride-to-be, 34, will wear a Monique Lhuillier design when she says her 'I do' to Toth, 40. "She's spending most of her time on that dress," a source tells the new  Us Weekly of the dress designer.

To ensure she looks gorgeous in the custom gown, Witherspoon has been breaking a sweat in 75-minute hot vinyasa yoga classes and added body scrubs and facials from Ona Spa to her routine.

As for the locale, the nuptials will take place at the star's Ojai, Calif. ranch. "The wedding will be in the early evening in one of the fields behind the house," reveals a pal.

For even more wedding day details, check out the latest issue of Us Weekly, out now.