Firstly, you don’t need ‘an’ in either of these, as you can’t count *your* shape in this context: it isn’t a countable noun. So you would just say ‘I’m in good shape’. Secondly, to answer your question, you can say ‘now’ or not say that: the first is the present tense so means generally now, at this time. You can add ‘now’ for emphasis or if you’re about to say something else, such as ‘but….. eg. Tomorrow I will quit the gym/ I’m about to have a baby/ who knows whether I will always be (in great shape)’. Hope this helps!

I am looking for a new apartment now I am looking for a new apartment

Adding now means that in the past you weren't. If you mean your physical condition is perfect, there should be no article in front of perfect. I'm in perfect shape (now).