I just started Step 4 too!
I too do not have a sponsor. I have been going to Al Anon meetings for about one month.
I haven't asked anyone to be my sponsor because I haven't connected with anyone else's story yet. I intend for this to be a long-term relationship...so I don't want to rush it.
However, that hasn't kept me from approaching Step 4. My philosophy is: I don't have to do this once, and perfectly.
I'm going to continue working the Step but I WANT to do it with a sponsor so I'll likely revisit the Step again (and again and again with my sponsor).
I would encourage you to start going to the meetings. I also started off on a solo operation. Let me tell you...the difference between reading the literature alone...and sitting in the meetings is HUGE.
I didn't notice significant change until I sat through the meetings.
I didn't notice BIG changes until I started sharing in the meetings.
I'm sure more seasoned members will chime in...