Size should not be an issue whether it's penis size or the size of you and your hubby.... bigger people can have perfectly normal sex... some positions can be a bit 'akward' or not achieveble though.
I would love to slip in behind my wife while we are lying on our side in bed, but my stomach and her butt get in the way and my penis is not long enough to penetrate her that way.
However, as others have suggested your husband may be able to please you in other ways - my wife loves it when I stimulate her clit with my fingers and she will always orgasm that way, so get him to stimulate you in other ways using his hands, mouth and or toys.
The one thing I would not do is come straight out and tell him sex does not satisfy you, because that may make him feel insecure...... my ex GF did that many years ago and it ruined our relationship (hence the reason she is my 'ex')
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