Jumping in because I just went through a similar thing and it was an amazing learning curve! I get really nervous about security with my main account, so I spent ages looking for the safest way to do this. I think someone told me that using the Wish List feature is the most secure way, though I am not 100% sure if it handles 40 items perfectly without some manual clicking. I love it when these things actually work out without compromising your data!!

• Try the Wish List method first since its totally free and native to Amazon
• Be super careful with browser extensions that ask for permissions to see all site data... I have heard some can be sketchy
• Always double check your cart total after importing because iirc prices can jump around during the move Its such a fantastic feeling when you finally get that bulk buy sorted without any glitches! Let me know if you want to chat more about keeping the account info safe.

i have dealt with this same headache before. the native tools are basically useless for more than one item. here is what works:

• Share-A-Cart extension: this is the most reliable one i have used for Amazon UK. it creates a code to sync the whole basket.
• CSV export scripts: some chrome extensions let you grab ASINs into a spreadsheet which is decent for bulk edits. for anyone shopping with friends or doing a gift list, Cart to Link is worth trying