All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The husband has the right to enjoy his wife sexually in any form of sexual enjoyment as long as he refrains from anal sex and intercourse during her menstruation. Allaah, The Exalted, says (what means): {Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish and put forth (righteousness) for yourselves. And fear Allaah and know that you will meet Him. And give good tidings to the believers.} [Quran 2:223] One form of lawful sexual enjoyment is for the wife to masturbate her husband, for instance. Please, refer to fatwa 87743.
The Muslim woman is obliged to respond to the request of her husband whenever he calls her to bed unless she has a valid reason for refusing, such as menstruation, postpartum bleeding, or severe harm, as we previously explained in fatwa 100429. The same ruling applies if she is preoccupied with performing a religious obligation; she is not obliged to respond to his request in this case as well. The Hanbali scholar Al-Buhooti wrote, "The husband has the right to enjoy his wife sexually in the vagina even if from behind her as long as no harm is incurred on her and it does not preoccupy her from performing a religious obligation..." [Ar-Rawdh Al-Murbi‘]
The fact that you experience pain during Ghusl (ritual bath) or lack sexual desire does not constitute a valid excuse that allows you to refrain from answering his call to bed.
If you endure significant harm by using water, then you are obliged to wash the sound body parts with water normally and wipe (perform dry ablution) over the rest of the body. Haashiyat Ibn Qaasim 'ala Ar-Rawdh Al-Murbi‘ reads, "If the person fears incurring harm on himself by using water in purification (ablution or Ghusl), then he should wash the sound body parts that would not be harmed by water and perform dry ablution for the rest so as to carry out the relevant obligation, without neglect or immoderation."
If you could not find any other way to help your husband guard his chastity yourself, then the solution is for him to have another wife. It is allowable for the Muslim man to take up to four wives if he is able to observe justice and equality among them. Allaah, The Exalted, says (what means): {...then marry those that please you of (other) women, two or three or four. But if you fear that you will not be just, then [marry only] one...} [Quran 4:3] It should be noted that taking a second wife may be obligatory on the husband in case he fears the temptation to commit immorality if he did not take another wife.
Ibn Qudaamah wrote, "As far as the religious ruling on marriage, people are of three categories: a person who fears the temptation of committing immorality for himself if he does not get married; it is incumbent on such a person to get married according to the majority of scholars because he is obliged to guard his chastity and shield himself from committing the unlawful, which is achieved through marriage..."
Shaykh Ibn ‘Uthaymeen wrote, "Hence, we believe that it is better and more prudent for the Muslim man to settle for one wife. However, if he believes that he would not be able to guard his chastity when marrying one wife only, then we advise him to take a second wife, or even a third and a fourth, until he attains serenity and becomes able to lower his gaze, guard his chastity, and find peace of mind..." [Zaad Al-Mustaqni']
For more benefit, please refer to fataawa 84026 and 81853.
Finally, your husband should be supported and helped to accomplish this objective, not face obstacles laid down by his wife or his sons or daughters.
Allaah knows best.