Replace retainers?

I got my braces off 3-4 years ago. I did wear my retainers at first. But I haven’t in about 2.5 years now. My top teeth are still straight looking. But my bottom teeth are just okay. Theyrenot bad. But I notice 1 tooth in particular moving ober and trying to twist in front of another. And a lot of them aren’t straight straight anymore. But some further back than others. Nothing too noticeable as it’s my bottom teeth.

The question, should I get a replacement retainer to prevent further movement and until I can afford Invisalign? Or just wait until I can get Invisalign. It’d be another 2 years before I could. My old retainer WILL NOT even halfway ago on.