flowers in between rows

Lavender, permanant and easy, I have a small area for flowers to attract all sorts

Get a dwarf cultivar - normal lavender gets to be quite a large plant (up to 3' tall, and easily that across).  Any sort needs a clip over in early autumn to keep it compact and neat, or you end up with a sort of scruffy standard - lots of growth on top, and bare stem for the first foot or so.

Alternatives (you don't want lavender between rows, as its roots will spread and get damaged each time you dig), are lots of annuals - poached egg plants (Limnanthes) are traditional and good for attracting bees and hoverflies, but almost any with single flowers will help.  They will self-seed, so either cut them before the seed heads open (and save the seed to plant next year if you want to), or let them do their thing and weed them out from where you don't need them.

i thought planting some flowers like marigolds keep pests away as well as adding color

Calendulas are a no-care, heavily flowering plant that really attracts the bees as it's a 'single' rather than double flower which bees prefer. Calendulas are annuals but readily self seed so you can actually 'weed' them out of places you don't want them and still have loads left. And if you step on the plants, you won't much care. The dried petals work nicely in some herbal tea mixes.
While I love lavender, I'd never put it in an area that's walked in as they really need dry conditions or they'll quickly go mushy and they can't tolerate stepping on.

Marigolds don't exactly keep pests away directly .............

From: http://www.dgsgardening.btinternet.co.uk/companion.htm

"Some plants exude protective chemicals (allelochemicals) from their roots or foliage which can deter pests, eg. African Marigolds produce thiopene which repels nematodes so it makes a good companion plant for root crops which are attacked by nematodes. This is given the title Allelopathy."

"Marigolds and Garlic have a reputation for repelling a number of insect pests such as Aphids and Carrot Root Flies. The Mexican Marigold, Tagetes minuta or Muster-John-Henry, is an annual which grows to about 1.2 m (the species name refers to the flowers not the height of the plant) The roots have an insecticidal effect on nematodes and some effect on keeled slugs. The secretions responsible begin about 3 months after sowing and also affect the growth of Ground-elder (Aegopodium podagraria), Bindweed (Convolvulus arvensis), Couch grass (Agropyron repens), Lesser Celandine (Ranunculus ficaria )and Ground Ivy (Glechoma hederacea). It is grown as a half-hardy annual which can be planted out after the risk of frost has passed, but this does not usually give them a long enough growth period to flower and set seed in Britain. Deadheading prolongs the growth for protection purposes."

Also check out:

http://www.gardenorganic.org.uk/pdfs/international_programme/TNP2-Mexican_marigold.pdf

I thought I'd read every possible theory on how to try and combat the dreaded bindweed but that's a new one! - which I think I might just try!  Thanks!