Need to balance my currency exposure, expenses are mainly in THB income in Euro.

Is there an Set index open to private investors? Cost?

Or would you , as one who doesn't know a thing about Thai companies invest in direct shares of the 5 best companies?

Which are?

Any good experience with fond managers?

There are many different types of Mutual funds available in the Thai market, you can find some offered by Bangkok Bank below...

Bangkok Bank Mutual Funds

Based upon your OP, I think you my be interested in the below fund...

Bualuang Top-Ten Open-end Fund

The Bualuang Top-Ten Open-end Fund is a medium to long term investment in the top ten stocks considered most likely to yield the highest total returns in the Stock Exchange of Thailand. At least 65% of the fund's NAV is allocated to equities while the rest will be invested in debt instruments, deposits, or other financial assets, as approved by the SEC.

Thanks, the Bualuang Top-Ten Open-end Fund may be just the thing I am looking for.

where do I find a chart comparing the performance?

Are there any comparable funds out of, e.g. Singapore, ??

Since you are to a large extent index tracking or planning to do so - why would you pay someone for doing that? Any alpha over the index you pay in fees. On average you're really just getting the beta (which you can easily generate yourself) less fund fees.

You might want to consider an exchange-traded fund (ETF) for Thailand e.g.

iShares MSCI Thailand Invest Mkt Index (THD)