P2P lending probably fits your criteria. I wouldn't put all of it in them, but some of it.
There are some sites which have very good records, eg
Loanpad
Capitalrise
Kuflink.
The first is 6.5%, 2 months access, the other two are higher rates but longer tie in. I have some money in all three and am happy with how they've gone.
For four years, some sort of bitcoin exposure makes sense, as you would expect to get a full cycle. PPINGTF but no one who has held bitcoin for four years has ever lost money
It's a high risk investment not covered by the £85k savings guarantee. Some of the early lenders went bust, there has been fraud and some people have lost their money.
Returns can be good but not something to do unless you are comfortable with the platform and understand the risks.
P2P lending probably fits your criteria. I wouldn't put all of it in them, but some of it.
There are some sites which have very good records, eg
Loanpad
Capitalrise
Kuflink.
The first is 6.5%, 2 months access, the other two are higher rates but longer tie in. I have some money in all three and am happy with how they've gone.
For four years, some sort of bitcoin exposure makes sense, as you would expect to get a full cycle. PPINGTF but no one who has held bitcoin for four years has ever lost money