Construction correct?

It should be ... qui est attaché... since the relative pronoun functions as the subject of the relative clause.

Thanks for the reply.  My confusion is that in my sentence, I thought "Je" was the subject and "le balcon" was either an object or something else.  Any insight on that or link reference you have that could help me understand would be appreciated.  Merci!

Je is the subject of the main clause and qui is the subject of the subordinate close. 

Je m'assieds dans une chaise sur le balcon. Il est attaché à mon appartement.

The second sentence gets attached to the first one by using a relative pronoun (qui), that stands in for the subject (it). 

Thank you.

Are the below two sentences correct uses of "que" & "ce qui"?

Je m'assieds dans une chaise que j'ai acheté au magasin

Je m’assieds dans une chaise sur le balcon, ce qui je trouve relaxant.

I see that i'm wrong.  To follow the lesson above, it should be the following?

Je m’assieds dans une chaise sur le balcon, ce que je trouve relaxant

Absolutely correct. I think you got it. 

Merci pour votre aide!