Well, how much are you able to spend? A randonee set up can be pricey—as much or more than your downhill skis, boots, and bindings. But it's worth the money: randonee skis, which are also known as alpine-touring skis, take the power and control of a good alpine setup and, with climbing skins, give you the ability to hike uphill cross-country style for the best snow. It's like heli-skiing, except you're the helicopter.
Volkl Gotama skis
Volkl Gotama skis
In any boot you buy, fit matters most. Most boots come with liners that a specialty shop can mold to your feet, but you'll still want to start out with the right fit. A solid mid-price choice is the Scarpa Maestrale ($599). They’re a lightweight, four-buckle boot. In fact, at under seven pounds per pair, they’re among the lightest all-terrain/randonee boots on the market. They’re also warm, well built, and offer excellent control on rough terrain.
You can spend more, of course. Garmont’s Radium AT boots ($750) are similar in materials and design to the Maestrales (four buckles; Pebax uppers). But they’re also heavier, running a pound more than the Scarpas. That will translate into tougher climbs, but the Radiums will feel more like your race boots—meaning you'll have more control—going downhill. In between are the the Black Diamond Quadrant AT boots ($650). Again, they come with four-buckles and Pebax uppers.
For skis, you have many more choices. Skis today have gone in two directions: super wide to float across powder, or with radical sidecuts to carve turns in more variable conditions. K2 has a lot of experience in this latter category, and their Backup ($625) is a well-priced alpine-touring ski. They're great on hardpack and crud, but still get by in soft snow.
You might also take a look at the Volkl Gotama ski ($750). Volkl made the Gotama's core with two types of wood, providing both stability and snappy performance. They're significantly wider through the waist than the Backups (106mm versus 82), a difference you'll notice immediately in powder.
Bindings will run you between $400 and $600, ranging from the Marker Tour f12 ($430) to the Dynafit TLT Radical FT ($600). Generally speaking, spending more on bindings will net you less weight and more performance. Skins should set you back about $175, and alpine touring skis all have attachment points to accommodate them.
I think you’ll find that a solid alpine touring package holds up against your downhill setup. Have fun!