Using bold, underline and italic is fine. As long as there is a purpose, you will not be penalised. Remember the golden rule, be natural. If it is necessary to underline a keyword, then do so, but don't do it just to optimise that keyword..

Personally, I think readers of content written in the first person are less likely to trust and like what is being conveyed. A person or company that talks about themselves is much less credible than that person or company being talked about by someone else. Show your clients examples of first-person writing vs. third-person writing and see which they prefer. As you say, client is boss.