What are simple ways to offer flat rate shipping for an online baby wear store?

Hi,

I’m about to launch my baby wear store next week (Littlecrusoe.com) and am completely confused over the simplest way to offer flat rate shipping options! I’m based in the UK. I’ve set up a business account with Royal mail click and drop, although can’t get click and drop to connect - Royal mail are looking into it as it seems to be an issue on their end. Anyway, i assume i can still use my Royal Mail business rates and advertise them at check out to then fulfill. I’ve also made use of the rates offered by shopify for the UK. I also only have the basic shopify package to begin with. Can anybody offer me advice on the best way to offer shipping/integrate it with your store, or am i doing things right so far? I don’t think i need to use a third party add on yet, or do i?! Also, what international shipping options do i have, apart from Royal Mail/Parcel Force?

Any reply and tips would be much appreciated!

Thank you