What drauk says about sticking to an easy flight is sensible, and works if you can guarantee that it will be an easy flight. But the trouble is that in any flight, conditions can change. The weather may deteriorate slightly, some little thing may go wrong with the aircraft, the circuit may get crowded, ATC may suddenly want to tell you lots of things.
These may all be things that you would take in your stride when you're flying regularly. But the longer you haven't flown, the more you have to concentrate on the actual mechanics of flying. And so you get overloaded more easily by something else - you simply don't have enough spare capacity.
For example, I remember flying one winter when I wasn't as current as I might have been, and the generator light came on. I stared at it stupidly for a bit, thinking, "What does it mean? What shall I do? Should I be worried". Of course, it didn't take long for me to realise that an electrical problem wasn't an emergency, but flying across the Pennines with it in the winter probably wasn't sensible, and that since I was ten minutes from the airfield, going back and sorting it out on the ground was the best idea. No big deal...though it shouldn't have taken me as long as it did. But suppose I'd been further away? Suppose at the same time I'd realised that the cloud base was lowering. Suppose in that minute or two that I was thinking, some other non-current pilot, head down in the aircraft, had approached......?
A trivial incident, you might say. YOU of course wouldn't be thrown by it, even if you hadn't flown for a while. Well, maybe you wouldn't. What do I know? But can you be quite sure?
So yes, if you really know your own abilities and limitations, your own reactions to stress and overload, exactly how quickly your capacity degrades after a lay-off, and precisely how much your thinking corresponds to your actual abilities, then fly alone. But still only do it on a day with good weather, when you're unlikely to have anything else go awry, and stay close to the airfield. But if you're not certain about any of the above, take an instructor, or at least another more current PPL as a safety pilot.
And if anything did go wrong, just think how it would look on the AAIB report........... he hadn't flown for a month, and he didn't have that many hours, but he FELT current, and he THOUGHT it would be OK........