I'm in exactly the same boat, and I'm tight for space.
I've been using two Aldi/Lidl workmates with 18mm ply offcut screwed down. I found that wobbley, so I put some recovered pallet planks down first and put the ply on top of that. I find laying more boards across the lower part of the workmates and putting toolboxes and stuff there really adds to the stability. I have made various plane stops, wedge clamps, etc. etc. to use with it. My huge big Record 52 1/2" vice (picked up for a song at a rural auction!) is sitting in a corner gathering dust until I get around to making a full-on bench.
AOK except for serious planing when I'm doing non-restoration projects, but not much call for serious planing in the furniture repair/restoration side of things. When I need more space, say if I'm working on a larger coffee table, I lay another larger sheet of 12mm ply on top, just temporarily.
What I really need is not a big bench, it's big clamps for gluing up entire pieces of furniture. That's where I'd spend my money. Damn they're expensive.