Good question,
There is no direct substitute for surfing; however, there are boards that get close. Many will claim to be the best snowboard or surf cross trainer but that is marketing BS! It all comes down to preference. I would suggest a longboard, with standard longboard trucks. (52 degree 180mm or similar) and any deck of your choice, it really is a preference thing if you are not into doing 113km/hr, and even then beyond the science, there is personal choice and riding style. For a newbie, it really doesn't matter. As for wheels, get longboard wheels not street skate wheels, they ride much smoother and are much grippier. (70 to 80mm would be my suggestion, nothing smaller! 78a or 80a durometer.... which is wheel hardness). If you're a bigger guy [apparently Diva Dude missed the part where you were a Ski Diva and therefore not a big guy], 200lbs plus, I would recommend 10mm axles in your trucks, and then of course 10mm bearings. The standard size is 8mm. The 8mm axles are always bending which make the board less stable. You may never notice if you're just cruising.
Always always always get a helmet and slide gloves!! Slide gloves are a work glove and high density plastic on the palms, ( or mom's old cutting boards ) WHEN you fall, not if... you will put your hands down, the slide gloves will protect your hands, AND will keep your shoulders from dislocating which is a common injury for those you dont wear SLIDE gloves. You can find these at shops, or make them your self..... google it, it's really easy and worth every cent. You will not regret your long board purchase, I have been riding with gents that STARTED once they retired. Its a great way to commute. With all that being said if it's only balance you're looking for, fill a 2 liter pop bottle with water, tighten the cap extra tight and lay it on the floor, then borrow the front of your mom's dresser drawers and dalance on the pop bottle! Any peice of wood will work if your mom is sensitive about her dressers. They are usualy oak and look super cool. This is called a homemade bongo board. They are good in the winter. But so is telemark skiing which is much cooler and life chaging. I recommend that! Good luck!
Ringrat's Diva Dude
[Ringrat doesn't recommend taking apart your dresser to make a bongo board.]