@Morshi , I can help you in this process without losing rank PM me for support.
In general, follow this procedure.
Before moving to https, you should analyze your site and take reports everyday for atleast 7Days before the date of shift. Here reports means, GTMetrix, Pingdom, Google page speed, SEMRush, Ahrefs, Majestic…
Normally we won’t concentrate on taking reports at very short interval, but here you should every 24hrs in your local time.
1.) Most of the people loose their ranking is because failed to update HTTPS shift in Google Webmaster’s.
2.) You should remember that you will have four different version of sites in your webmasters.
2.1.) http non-www
2.2.) http www
2.3.) https non-www
2.4.) https www
Note: if you are using http www, then you should shift to https www. Cross linking will cause issue.
3.) First two days are so vital after shifting, you should analyze your site with as much tools you have in your SEO list.
3.1.) Canonical links
3.2.) Broken Links
3.3.) Redirection links
3.4.) Internal links [A very hectic process here]
3.5.) Other 3xx, 4xx, 5xx links.
4.) Update the new sitemap in https property and do not delete old sitemap immediately after updating new one.
5.) Update Disavow with URLs pointing to https to let Google know your shift.
6.) Re-edit all articles to add https to Image links, Internal links and DO NOT USE PLUGINS. Many people loose their ranking because of using these kinds of plugins. You should do it manually.
Monitor, Monitor, Monitor is the solution to solve most of the problem.
Hope, prepare a plan and work out. All the best.