A.K.
Mama-guilt. It just keeps giving and giving, doesn't it!
We try to go for walks or bike rides (we have a burley that we love) as much as possible after work, if the weather is bad we sometimes play "marching band parade" around the house (which baby might find pretty funny), playing musical instruments and marching around.
To make yourself feel better, can you schedule a time, once a week or so, where it's just you and him? make a big deal out of it and call it "mommy and ______ morning" and make it a consistent time you can do something fun together. I work 4 days a week and have Mom&Mya day every Friday. I'm sure it is good for her, but I KNOW it is good for me... that MamaGuilt is a killer. I'm pregnant now, so I will be in your same situation soon....
Here are a few things we have found to do with our almost 4 year old, maybe some of these you can do while breastfeeding and/or cooking. Also, keep in mind that at daycare(?) he is playing with other kids the entire day, a little down time of playing by himself with his own toys (while you do busy work) might actually be welcome to him.
Family Time Fun Beginner Dinner Games
by FamilyTime Fun
http://www.amazon.com/Family-Fun-Beginner-Dinner-Games/dp...
ThinkFun Zingo
by Think Fun
http://www.amazon.com/Think-Fun-7700-ThinkFun-Zingo/dp/B0...
Orb Factory Magnetic Mosaics Kids
by Orb Factory
http://www.amazon.com/Orb-Factory-Magnetic-Mosaics-Kids/d...
Cranium Hullabaloo DVD Amazing Animal Adventure
by Cranium
http://www.amazon.com/Cranium-Hullabaloo-Amazing-Animal-A...
Richard Scarry Busy Town
by I Can Do That Games
http://www.amazon.com/Can-Do-That-Games-01017/dp/B002V3RC...
and don't forget PLAYDOH!
GOOD LUCK MAMA! don't let the guilt get you down.