Jodi,
I have one sibling... who is 12 years younger then I. So... essentially I was an only child. I think it is completely possible to raise a loving, caring, thinking of others child whether you have 1 or 18 like the Duggars!
First, I want to say, I think your son's personality would be like this whether you had another child or not. In my opinion, having a 'needy' child has nothing to do with whether they have siblings or not. A friend of mine has 4 children, no one child has a personality like the others. Each is very unique and very different from their siblings.
That being said... I think Amy has really hit the nail on the head. Your son just needs to be around you more. There is really nothing wrong with that actually. Try to encorporate ways your son can be near you more often. Also, as Amy suggested... model good behavior. If, when you are done working, you show your son 'when mommy is finished I put my things away'.... then he too will learn that is the appropriate thing to do. Also, having someonoe to help pick up toys is not really a bad thing. Work is always more fun and less 'work' when there are more helping hands.
I have to say, I love my mother dearly...she is my mother... but very very early on I learned she would not play with me. She was not going to be any kind of companion for me. Her soap operas, books, and other interests were just more important. It was always 'we'll do it later' ... and later never came. Consequently I was a very very independant child. I played well by myself for hours on end. However, once in school it was very hard for me to make friends. I never had many. Even now... I have maybe 2 or 3 people in my life whom I consider 'friends'. I can get along with just about anyone in any situation... but I am very 'arms reach' with most people.
Later, when I was older and stretching my preverbial wings more... I became even more detached from my mother. Then, she wanted me close. It never happened. Even now, I know there are times she grieves the relationship we never had. But, it was the choice she made. I now make a conscious effort to have my daughter around me as much as possible. Even though I will take time for 'me' to catch up on e-mails and what not... even when I am doing that... my daughter is playing near me. I take time every day to play with her and let her know she is important.
My sister, as I mentioned is 12 years younger then I. She had me, yes. My mother, although she attended to my sister a bit more... was still distracted by her own life to a large extent. But, because my sister had me to step in ... and even at times call my mother on her actions... she grew up in a very different environment. She is very social. She has many many friends and although she does not open herself to everyone ... she is more 'adjusted' at her age then I was. She has told me directly that the person she is... was molded by me more so then by our mother.
My point is... your little boy is only a little boy for so long. Take the time to be with him. Learn his needs and together you can find a way to help him grow into a strong, caring, wonderful man. Providing a consistent, caring, nurturing, loving and attentive environment will help him achieve all he is meant to be.