How to handle redirects when moving site to Squarespace

I am in the process of moving a site that I built for my wife from another hosting company to Squarespace.  We will be starting the domain move this weekend.  The old site is currently indexed by Google.  I have both pages that will be part of the new site and others that will not.  My question is how I handle page redirects.  Do I make changes to the sitemap.xml file on the old site as well as make changes on Square space.  The pages I'm most concerned about are the inventory pages which will go from a structure that looks like this: http://www.domain.com/inv_neck_ckd.php
To this: https://domain.com/shop/necklaces

I know that I need to make changes, I'm just not sure where to do that.  Any guidance is greatly appreciated.

Hi @Skor - we published a guide to managing redirects when migrating a site to Squarespace that covers this topic which might be helpful: https://www.bluehillsdigital.com/articles/squarespace-migration-seo-rankings

You will need to be careful to set up 301 URL redirects for all pages/posts on your website that will move to a different URL after the migration. The post linked above includes a guide about how to generate those URL redirect rules using a formula in a spreadsheet!

You don't need to make changes to the sitemap on the old website, because after the domain is point to the Squarespace site that old sitemap will no longer be accessible to search engines. 

Squarespace generates a sitemap automatically for every site, which is accessible by just adding .../sitemap.xml to the end of your site URL.

After you finish the migration, it would be a good idea to submit the sitemap in Google Search Console, to encourage Google to re-index the new site and take note of all the changed page URLs.

Feel free to get in touch if you need assistance with the move!

Great, thanks @edharrisfor your guidance.  I plan to work on it this afternoon and will reach out if I run into any problems.

One quick question though.  Do I need to add a line item for the the home page which on the old page was index.php?

No problem @Skor and yes, I'd recommend including an explicit redirect rule in the new website for the homepage that looks like this:

/index.php -> / 301

This would make sure that if there are any backlinks to the website from elsewhere on the web that include the index.php path those links would still resolve to the new homepage after the migration.

Thanks so much @edharris.  Starting the process now.