Take a look at the Combobox widget.
https://docs.mendix.com/appstore/widgets/combobox/
I know you said you didn't want to use a widget from the Marketplace, but this is written by Mendix and has full platform support. Mendix will support you with any issues you have with this module as part of your SLA.
https://docs.mendix.com/appstore/marketplace-content-support/#category
I hope this helps.