Not that this is a realistic event anyway, but I always laugh at most of these armour suggestions.
Put on some plate armour and then go jogging for an hour at a steady pace on a hot day. Then fall down and try to get up by yourself. Keep in mind you won't go through a hoard of zombies with a sword in less than an hour.
Now get some SWAT gear and go to a personal trainer and pay him extra to put you through a full aerobics workout and see how long until you pass out from dehydration.
Keep in mind pro athletes who wear protective gear are rarely in play for longer than 4-5 minutes at a time. But it's probably your best bet to go with the lightest weight hardpoint armour you can find that is breathable, likely hockey gear. Mix it with ballistic nylon/kevlar motorcyle gear that is breathable and flexible. Anything that is lighter and more breathable that can be substituted is an improvement. There is great gear for mountain biking that won't be too hot, but it doesn't cover 100% of the body.
Zombies don't shoot back, nothing has to be bulletproof, it has to allow free movement, not weigh you down, and not overheat you. The protection should be enough to protect from a large dog bite, or a rolling fall down a rough hillside.
Add a camelpack for water, which won't last forever, you have to figure on moving in and out fast, taking out a few each time. Full lightweight Coolmax underwear to keep you cool and prevent chafing. Boots can be lightweight workboots with composite armour soles and toes, or similar police issue or army surplus.
Leather will make you sweat like crazy, again try jogging in anything you have in mind, or at least imagine it.