Langely,
Having been thru similar circumstances with similar partners - I can attest that what you face are essentially a breaking down of barriers brought about as lifelong recriminations for previous experimentations during your partners' early life.

Can you change them? Unless they were traumatized thru rape or Abuse, You can - but it will not happen OVERNIGHT, and certainly, closer to a few months... and even that, may not amount to as much change as you want.

First things first... Their attitudes to what you want to try in the bedroom, will require YOU to change.

Women tend to suffer greatly from LOW self-esteem.

What you will have to do is bolster their low self-esteem by offering them small compliments, from time to time... followed closely (before and AFTER the compliments), by admiration on your part, for anything they've done that is similar to what you want them to do for you.

If you want her to wear sexy underwear... make remarks of how good you think she looks in her clothes, underwear, etc. Hold your Compliments for her until AFTER you show her a beaming smile.. whereby she will ask you WHY you're smiling. THEN you tell her your compliment.

Start small and try NOT to over do it ... "I love how you look in that dress".... or "That bra makes you look simply delicious".

Ignore the fact that it may sound silly or Cheesy to you. You have to mean it and your body's posture, your eyes, even your arms all have to say the same thing.

Imagine that you just saw her in the most sexiest of underwear, and you will project the right attitude.

If you've never complimented her taste in clothes, her body, or even her looks - you will have to start with even smaller compliments... and with varying frequency so that she doesn't get suspicious.

If she DOES get suspicious... tell her something like you've reminded of why you first fell in love with her, etc.

Follow this behaviour with small gifts, in line with the subject of your compliments. Include a note that says something like: "I thought of you when I saw this....", or send her flowers, unexpectly, with a note that says "I love you".

If you DO send flowers, remember a few flowers or a small bouquet says "thinking of you".. whereas a dozen or more flowers says "I'm feeling guilty".

Over time, buys her gifts related to what you want her to wear... and all the while, compliment her on her tastes in underwear.. but leave room for criticism - say something like: "I like what you're wearing... Have you ever considered wearing something more daring (or sexier) that would really compliment you?

Now, don't quote me exactly... these compliments have to be in your words.. and in your way of thinking.

Good luck