Adding Options with price variations?

[aamcle]

I have a product (Prod1) with a Price P1.

What I want is for customers to be able to choose from a drop down list and add options AND for that choice to update the price so
(Prod1 + Opt1) to update the price (P1 + Opt1 price)
(Prod1 + Opt2) to update the price (P1 + Opt2 price)
(Prod1 + Opt3) to update the price (P1 + Opt3 price)
and so on - standard stuff sorry ...........

So I create a custom field as a parent field and custom fields for options as it children, I select the appropriate custom field type under the Product save it and the custom fields display.

What "types" should I have chosen to make it actually work?  I tried "Cart Variant"  but it didn't seem to do anything.

I'd also like the choice of options to be displayed near the "add to cart" button not at the bottom of the items description.

I've looked over what documentation exists and as usual not understood it and I'd really appreciate any help you are willing to give.

Many Thanks             aamcle