You could be sowing these at the moment – Chinese Leaves : Richi F1 (Seeds)
Chinese Leaves are quick maturing and form a cos lettuce type heart in under 9 weeks. Plants are very slow to bolt, so stand well over a long season. Use as salad leaves as you would a Romaine lettuce or as a full heart for salads, stir fries and as a cooked vegetable.

Sow thinly in well prepared soil, 13mm (½in) deep in rows 38cm (15in) apart. Keep soil constantly moist to prevent seedlings bolting and to deter flea beetle which can pepper holes in the leaves.

Well worth trying some of these in the empty beds as you’ve eaten the crops you’ve already grown!

You could also be planting this now – Corn Salad Cavallo
Which crops in 50 Days – Salad Leaves : Corn Salad Cavallo (Seeds)
Corn Salad Cavallo keeps on producing a mass of fresh flavoured, deep green ‘lamb’s lettuce’ leaves. A late summer sowing will guarantee winter salads.
You simply sow seeds at fortnightly intervals from late summer to late autumn in a sunny position and well drained soil which is in good heart. Sow seeds in drills 12mm (½in) deep and 15cm (6in) apart. Water the young plants during dry spells.