I found this really useful book set on a second-hand market stall in the summer. I felt it was worth a look for £3.
It is Aba-Conundrums by Evelyn B. Christensen, published by Fat Brain Toy Co. The set includes a soroban, 120 number puzzles (& solutions) on spiral-bound dry-wipe card and dry-wipe pen.
The problem solving elements of the tasks are really good for improving basic number skills.
After boring four generations of my family with it, I did a bit of web-searching and came across the Soroban Cymru website – don’t worry if you don’t ‘siarad Cymraeg’, it’s in English.
I think proper use of sorobans could be a really useful tool for developing the understanding of number in low ability Year 6/7. I know they are used by all abilities in Asia, but pupils here don’t generally know how to use a soroban correctly and it could be a way to make numbers more interesting for those who disconnected from maths at a young age. I’m certainly going to try it out this term.
You can get basic sorobans on Amazon from about £2.50.