I understand, I've been through the same experiences. Having a reading plan is the better way to go for perfectionists like myself. A reading plan gives a target to shoot for. Having a target or goal spurs us on to read more than if we left it up to our mood.
The biggest problem is like you said, what if I get behind. Its not so much missing a reading that is the problem, its the expectations we place on ourselves. If we read 5 days out of 7, we think we are behind by 2 days and need to catch up. What I've done to combat that perfectionism is to reverse the perspective. Instead of seeing myself as behind by 2, I look at it the other way - I are now ahead by 5 days. Does God know I'm not perfect? Certainly. Does God care more about what I've read - the 5 days - more than the 2 days I've missed? Absolutely.
So what happens to the 2 "missing" days? I either
1) extend my reading plan out 2 more days, or
2) read a little extra here and there and eventually catch up.
Its really a focus on the completion of the plan rather than the timing of it. In all my years of Bible reading plans, I've never hit the original "time" target. But I've finished nearly all of my Bible reading plans. No one says you can't turn a one-year Bible reading program into 13 months or 15 months or even longer. The most important part is that you are actually reading the Bible.
By focusing on the progress toward completion, I give myself positives to continue with the reading plan without the pressure of guilt. Falling behind is relative - what I want to do is finish the race. I strive to read 7 days, but I'm not going to beat myself up for days I've missed. I've used this flexible plan approach to all my Bible reading for many years now, reading through multiple (English) Bible versions.
Also related to this is the approach to Scripture itself. If you want to read the Bible in a year, then that averages about 3-5 chapters a day. That even has missed days built into it. Are you wanting to get a broad overview or "bird's eye view" of the Bible or a Bible book? That means you will be reading at a faster clip, and multiple chapters at a time. Most people look at a book like Isaiah and see its a very long 66 chapters. I look at Isaiah and see it as a week of Bible reading - that is, I like to read it at 10 chapters a day. For many people, a 2 week reading at 5 chapters a day is a "doable" deal. Are you wanting to read Scripture carefully and take in the details? Then you will be reading fewer chapters more slowly, even taking time to stop to think and take notes. The reading plan might be 1 Peter for a month - that's only 5 chapters in 30 days, but the depth of knowledge you gain from slow reading the 5 chapters will be invaluable.
And another related issue is the moods obstacle. I'm a paradox - I absolutely love reading Scripture, but I quite often just don't feel like reading. But once I begin reading, then the obstacles go away and my love of reading Scripture is rekindled. Reading Scripture is kind of like exercise. Most of us are reluctant to start, but once we begin, something kicks in and we do it.
LDG