Just wash your 2yr olds hands a lot! Make sure he is not near the baby or breathing on him. No toys that he has should go into baby's mouth. Give him rest, fluids and love.
Your nursing, so baby is getting a natural immunity ~ usually this lasts for about three months. Not fool-proof, but it's there so eat healthy for the both of you. (you can still nurse if you get sick, but take your precautions, too so as to avoid it.)
I would actually wipe things down with a diluted bleach solution (a gallon of water and a tablespoon of bleach will do it.). If you have a spray bottle - that helps or just put it in a milk jug and pour onto a sponge and wipe. This way, you also avoid the excess costs of the wipes. (Sorry... it may not be too safe for the environment, but is less to toss into a landfill.)
Make sure after touching your 2yr old, that you wash your hands - just common sense stuff, really.
Biggest thing: Don't freak out. Don't stress over it as that can lower your immunity. Make sure all of you rest and get enough sleep to stay well. You will be fine~
Congrats on the new baby!