Unfortunately you can't ban someone from a funeral in a church (or a wedding for that matter) as it's a public place.
Near us an enterprising chap has built a recreation of a Neolithic burial mound and you can book a niche there for your ashes. DH had a cousin who had a woodland burial 20+ years ago and it was lovely. The site was new and the idea was to plant a tree over the grave so that the site would eventually become a wood.
Another friend's mother died last year and is buried on a hillside in Somerset, in a new 'green' burial site, in a wicker coffin.
Do some online research and I'm sure you'll find similar options. Can't offer any advice on how to deal with Mrs Busybody tho!
Forgetting where you left your keys does not mean you are “losing it”