A few thoughts:
The principle of Charity, as taught in the scriptures and particularly in the Book of Mormon, like many principles of the Gospel has multiple meanings.
The pure love of Christ can mean to have pure love for Christ as our Redeemer. The pure love of Christ can mean to love and serve others as Christ would do. That seems to be the type of Charity to which you are referring. Another meaning of Charity is to enjoy the pure love of Christ for us-individually- as we partake of the blessings of His Atonement and more importantly feel His love for us. Our physical or mental ability to serve others has little to do with Christ's love for us individually. We can enjoy true Charity in our lives regardless of our ability to serve others as we desire.
As for allowing others to help you....
I have heard the apostles (Elder Bednar?) talk about one of the defining characteristics of Christ- his ability to put aside his own suffering and reach out to help another. It happened when after betrayed, arrested and led with a rope around his neck, he reached out in mercy to restore the ear that Peter had cut off. It happened when on the cross, he reached out to make arrangements for the welfare of his mother.
Recently, a member of my ward was in a serious accident. This couple's first request to me was that ward members not be informed, as they did not want visitors, well-wishers or meals brought in. They are good people, but have tended to live the gospel on their own terms. I of course respected their wishes, but I was a little saddened at their request. Many ward members would have been grateful for the opportunity to serve. Here was an opportunity for them to emulate the Savior. In spite of their difficulties, they might have reached out to others and given them a chance to serve and to love as the Savior would - to show charity.
You may be physically restricted from serving others, but perhaps you can serve them by allowing them to serve you. You obviously know the joy of helping others - why not give others the blessing of also knowing that joy by serving you?
....another way you can serve with limited mobility - write notes/letters to ward members, family, friends. Pray about what others might need to hear. You may be a messenger of Charity to someone who is struggling.
Our greatest growth come during our toughest times.