Got it to work...
The drop down lists of options can be made from the recordsets no problem before choosing the 'add to cart button' behaviour.
Once in the Add to cart button panel, I added the custom fields to the list and then selected the OptionName from each recordset for the respective field.... checking the box 'updatable' creates hidden fields in the form that 'should' contain the values of the options.
However to make this work I had to delete these hidden fields and subsititute them for the drop down menus made previously... using the same 'name' descriptions given to the hidden fields i.e. 'eCart1_2_Size_Add' and 'eCart1_2_Colour_Add', ove this was done it passed the values to the cart just fine.
All good so far, I got to say though I think the documentation on ecart is a little thin. A thumbs up so far all the same.
Thanks for your help - (will probably add to this thread again today with more queries)