Using several domains on one website

Pointing both domains to the same location or using a 301 redirect.

[jecasc]

I have a website and started a shop on the same topic. The websites name was example.com, the shop is running under example-shop.com

The original website is no longer in existence, however the shop is running very well. For better branding I want to promote the shop with the name "example.com" in the future.

However the domain example-shop.com is ranking very well in Google and I do not want to loose that ranking.

The question is: How to do this best without loosing my rankings.

Since both domain names are related I thought about leaving example-shop.com as it is, and simply redirect example.com to the shop page. So in the Search Engines the shop will be listed with example-shop.com but people would be able to reach it by typing in example.com.

I have the following question:

I expect that people placing links in the future would directly link to "example.com".

How will this affect my rankings in Google in the future if

1. I simply point both domains to the same location

2. I use a 301 redirect from example.com to example-shop.com

3. I use a 301 redirect from example-shop.com to example.com