The safety is quite an upgrade if that is what you are concerned about. But literally the newer you go the better the safety equipment gets. Volvo is usually pretty high up there as far as safety ratings as a brand overall as well. The one you provided in the link has quite a few miles on it though and the new volvos aren't necessarily known for reliability.

Is it possible to get a Lexus instead of Volvo?

Your Jeep XJ is a certified 'Off-Road' vehicle while the Volvo XC90 is an all wheel drive SUV not meant for or designed to be used off road. Sure, you could probably be okay on the occasional dirt or gravel road but if you are into serious off roading I would not recommend it. If you do decide on a XC90, be wary of anything from 2003-2006 with the 2.9L T6 (inline 6 cyl.) engine as this model is known to have catastrophic transmission failure from as early as 30,000 miles. Remember, the Volvo is an European luxury brand therefore parts & repairs will be comparable to an Audi, BMW or Mercedes-Benz.

As Yaser stated above, depending on your budget, a more reliable and yet safer alternative would be a Toyota or Lexus large SUV such as a Toyota Highlander or Sequoia; or the comparable Lexus RX or LX models. Avoid Hybrid models with high mileage. Good luck!